Обсуждение: 12.2: Why do my Redo Logs disappear??
Hi all, this is a 12.2 Release on FreeBSD 11.3. I am doing RedoLog Archiving according to Docs Chapter 25.1. During the last week I have lost 4 distinct Redo Logs; they are not in the backup. Loosing a RedoLog is very bad, because there is no redundancy, loosing a single one of them makes the timeline disappear and it will only reappear after another Base Backup. Very very bad. So I did analyze the matter. There are three ways to restart a Berkeley machine: 1. Cowboy it (aka pull-the-plug). This makes sure that everything is certainly dead immediately, and, given all hard- and software is well designed, nothing bad should happen. 2. Shut it down. This is the official means, and it takes very long, because each and every applications are signalled and given time to bring up whatever objections they may have. In this case "pg_ctl stop" will be invoked with whatever options the sysop has configured, and postgres will copy out a full log into archive before terminating. 3. Halt/Reboot it, like this: https://www.freebsd.org/cgi/man.cgi?query=reboot&sektion=8&manpath=FreeBSD+11.3-RELEASE This is considered more safe than pull-the-plug, and still fast. Applications are killed without much waiting, but all disk buffers are flushed to permanent storage and filesystems closed. In this case, it seems, Postgres will delete the current log without archiving it. :( What precisely happens (according to the OS sources) during reboot is this: processes will be sent SIGTERM, and after some 2-10 seconds followed by SIGKILL. -------------------------------------- Lets have a closer look: We did a regular shutdown at 17:09, and then we did a reboot at 19:24. Here is the content of the staging area (where the logs are copied to and accumulated until it is worth to run a backup job): # dir arch/ total 240 drwx------ 2 postgres postgres 5 Jun 8 17:09 . drwxr-xr-x 6 postgres postgres 7 Jun 8 17:09 .. -rw------- 1 postgres postgres 16777216 Jun 8 09:38 0000000100000017000000FC.ok -rw------- 1 postgres postgres 16777216 Jun 8 10:48 0000000100000017000000FD.ok -rw------- 1 postgres postgres 16777216 Jun 8 17:09 0000000100000017000000FE.ok And here is the pg_wal directory: # dir data12/pg_wal/ total 89256 drwx------ 3 postgres postgres 10 Jun 8 19:28 . drwx------ 19 postgres postgres 23 Jun 8 19:28 .. -rw------- 1 postgres postgres 335 Jun 7 07:36 0000000100000017000000EF.00000060.backup -rw------- 1 postgres postgres 16777216 Jun 8 19:38 000000010000001800000000 -rw------- 1 postgres postgres 16777216 Jun 7 07:17 000000010000001800000001 -rw------- 1 postgres postgres 16777216 Jun 7 07:17 000000010000001800000002 -rw------- 1 postgres postgres 16777216 Jun 7 07:17 000000010000001800000003 -rw------- 1 postgres postgres 16777216 Jun 7 07:17 000000010000001800000004 -rw------- 1 postgres postgres 16777216 Jun 7 07:36 000000010000001800000005 drwx------ 2 postgres postgres 3 Jun 8 17:09 archive_status # dir data12/pg_wal/archive_status total 23 drwx------ 2 postgres postgres 3 Jun 8 17:09 . drwx------ 3 postgres postgres 10 Jun 8 19:28 .. -rw------- 1 postgres postgres 0 Jun 7 07:36 0000000100000017000000EF.00000060.backup.done Now where the hell is my "FF" log ??? Lets check syslog - this was the full shutdown at 17:09: Jun 8 17:09:38 <local0.info> admn pg-bck[73534]: [10-1] :[] LOG: 00000: received fast shutdown request Jun 8 17:09:38 <local0.info> admn pg-bck[73534]: [10-2] :[] LOCATION: pmdie, postmaster.c:2780 Jun 8 17:09:38 <local0.info> admn pg-bck[73534]: [11-1] :[] LOG: 00000: aborting any active transactions Jun 8 17:09:38 <local0.info> admn pg-bck[73534]: [11-2] :[] LOCATION: pmdie, postmaster.c:2813 Jun 8 17:09:38 <local0.debug> admn pg-bck[73549]: [10-1] :[] DEBUG: 00000: logical replication launcher shutting down Jun 8 17:09:38 <local0.debug> admn pg-bck[73549]: [10-2] :[] LOCATION: ProcessInterrupts, postgres.c:2981 Jun 8 17:09:38 <local0.info> admn pg-bck[73534]: [12-1] :[] LOG: 00000: background worker "logical replication launcher"(PID 73549) exited with exit code 1 Jun 8 17:09:38 <local0.info> admn pg-bck[73534]: [12-2] :[] LOCATION: LogChildExit, postmaster.c:3657 Jun 8 17:09:38 <local0.info> admn pg-bck[73544]: [13-1] :[] LOG: 00000: shutting down Jun 8 17:09:38 <local0.info> admn pg-bck[73544]: [13-2] :[] LOCATION: ShutdownXLOG, xlog.c:8321 Jun 8 17:09:45 <local0.info> admn pg-bck[82223]: RedoLog.bck invoked pg_wal/0000000100000017000000FE 0000000100000017000000FE Jun 8 17:09:45 <local0.info> admn pg-bck[82223]: RedoLog.bck pg_wal/0000000100000017000000FE 0000000100000017000000FE returns0 Jun 8 17:09:45 <local0.debug> admn pg-bck[73547]: [8-1] :[] DEBUG: 00000: archived write-ahead log file "0000000100000017000000FE" Jun 8 17:09:45 <local0.debug> admn pg-bck[73547]: [8-2] :[] LOCATION: pgarch_archiveXlog, pgarch.c:675 Jun 8 17:09:55 <local0.info> admn pg-bck[73544]: [14-1] :[] LOG: 00000: checkpoint starting: shutdown immediate Jun 8 17:09:55 <local0.info> admn pg-bck[73544]: [14-2] :[] LOCATION: LogCheckpointStart, xlog.c:8362 Jun 8 17:09:55 <local0.debug> admn pg-bck[73544]: [15-1] :[] DEBUG: 00000: performing replication slot checkpoint Jun 8 17:09:55 <local0.debug> admn pg-bck[73544]: [15-2] :[] LOCATION: CheckPointReplicationSlots, slot.c:1078 Jun 8 17:09:55 <local0.info> admn pg-bck[73544]: [16-1] :[] LOG: 00000: checkpoint complete: wrote 0 buffers (0.0%); 0WAL file(s) added, 1 removed, 0 recycled; write=0.000 s, sync=0.000 s, total=10.131 s; sync files=0, longest=0.000 s, average=0.000s; distance=16383 kB, estimate=16383 kB Jun 8 17:09:55 <local0.info> admn pg-bck[73544]: [16-2] :[] LOCATION: LogCheckpointEnd, xlog.c:8435 Jun 8 17:09:55 <local0.info> admn pg-bck[73534]: [13-1] :[] LOG: 00000: database system is shut down Jun 8 17:09:55 <local0.info> admn pg-bck[73534]: [13-2] :[] LOCATION: UnlinkLockFiles, miscinit.c:859 So, "FE" was copied out okay, and we have it in the staging area. And here is the relevant stuff from the following startup - here we consequentially are within the "FF" log: Jun 8 17:15:38 <local0.info> admn pg-bck[6366]: [8-1] :[] LOG: 00000: database system was shut down at 2020-06-08 17:09:55CEST Jun 8 17:15:38 <local0.info> admn pg-bck[6366]: [8-2] :[] LOCATION: StartupXLOG, xlog.c:6242 Jun 8 17:15:38 <local0.debug> admn pg-bck[6366]: [9-1] :[] DEBUG: 00000: checkpoint record is at 17/FF000024 Jun 8 17:15:38 <local0.debug> admn pg-bck[6366]: [9-2] :[] LOCATION: StartupXLOG, xlog.c:6532 Jun 8 17:15:38 <local0.debug> admn pg-bck[6366]: [10-1] :[] DEBUG: 00000: redo record is at 17/FF000024; shutdown true ---------------------------------------- From the fast reboot @ 19:24 noting at all is logged. At the following startup, we see that we are still within the "FF" log: Jun 8 19:28:24 <local0.debug> admn pg-bck[6465]: [1-1] :[] DEBUG: 00000: registering background worker "logical replicationlauncher" Jun 8 19:28:24 <local0.debug> admn pg-bck[6465]: [1-2] :[] LOCATION: RegisterBackgroundWorker, bgworker.c:854 Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [2-1] :[] LOG: 00000: starting PostgreSQL 12.2 on i386-portbld-freebsd11.3,compiled by gcc9 (FreeBSD Ports Collection) 9.3.0, 32-bit Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [2-2] :[] LOCATION: PostmasterMain, postmaster.c:997 Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [3-1] :[] LOG: 00000: listening on IPv4 address "0.0.0.0", port 5433 Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [3-2] :[] LOCATION: StreamServerPort, pqcomm.c:590 Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [4-1] :[] LOG: 00000: listening on Unix socket "/tmp/.s.PGSQL.5433" Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [4-2] :[] LOCATION: StreamServerPort, pqcomm.c:585 Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [5-1] :[] LOG: 00000: ending log output to stderr Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [5-2] :[] HINT: Future log output will go to log destination "syslog". Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [5-3] :[] LOCATION: PostmasterMain, postmaster.c:1297 Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [6-1] :[] LOG: XX000: could not send test message on socket for statisticscollector: Permission denied Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [6-2] :[] LOCATION: pgstat_init, pgstat.c:486 Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [7-1] :[] LOG: 00000: trying another address for the statistics collector Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [7-2] :[] LOCATION: pgstat_init, pgstat.c:418 Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [8-1] :[] LOG: 00000: database system was interrupted; last known up at2020-06-08 17:25:38 CEST Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [8-2] :[] LOCATION: StartupXLOG, xlog.c:6267 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [9-1] :[] DEBUG: 00000: checkpoint record is at 17/FF01BFE8 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [9-2] :[] LOCATION: StartupXLOG, xlog.c:6532 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [10-1] :[] DEBUG: 00000: redo record is at 17/FF01BFB4; shutdown false Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [10-2] :[] LOCATION: StartupXLOG, xlog.c:6609 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [11-1] :[] DEBUG: 00000: next transaction ID: 18955154; next OID: 145913 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [11-2] :[] LOCATION: StartupXLOG, xlog.c:6613 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [12-1] :[] DEBUG: 00000: next MultiXactId: 1; next MultiXactOffset: 0 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [12-2] :[] LOCATION: StartupXLOG, xlog.c:6617 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [13-1] :[] DEBUG: 00000: oldest unfrozen transaction ID: 479, in database13777 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [13-2] :[] LOCATION: StartupXLOG, xlog.c:6620 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [14-1] :[] DEBUG: 00000: oldest MultiXactId: 1, in database 1 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [14-2] :[] LOCATION: StartupXLOG, xlog.c:6623 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [15-1] :[] DEBUG: 00000: commit timestamp Xid oldest/newest: 0/0 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [15-2] :[] LOCATION: StartupXLOG, xlog.c:6626 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [16-1] :[] DEBUG: 00000: transaction ID wrap limit is 2147484126, limitedby database with OID 13777 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [16-2] :[] LOCATION: SetTransactionIdLimit, varsup.c:408 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [17-1] :[] DEBUG: 00000: MultiXactId wrap limit is 2147483648, limitedby database with OID 1 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [17-2] :[] LOCATION: SetMultiXactIdLimit, multixact.c:2267 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [18-1] :[] DEBUG: 00000: starting up replication slots Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [18-2] :[] LOCATION: StartupReplicationSlots, slot.c:1114 Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [19-1] :[] LOG: 00000: database system was not properly shut down; automaticrecovery in progress Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [19-2] :[] LOCATION: StartupXLOG, xlog.c:6764 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [20-1] :[] DEBUG: 00000: resetting unlogged relations: cleanup 1 init0 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [20-2] :[] LOCATION: ResetUnloggedRelations, reinit.c:55 Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [21-1] :[] LOG: 00000: redo starts at 17/FF01BFB4 Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [21-2] :[] LOCATION: StartupXLOG, xlog.c:7035 Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [22-1] :[] LOG: 00000: redo done at 17/FF01C098 Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [22-2] :[] LOCATION: StartupXLOG, xlog.c:7297 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [23-1] :[] DEBUG: 00000: resetting unlogged relations: cleanup 0 init1 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [23-2] :[] LOCATION: ResetUnloggedRelations, reinit.c:55 Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [24-1] :[] LOG: 00000: checkpoint starting: end-of-recovery immediate Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [24-2] :[] LOCATION: LogCheckpointStart, xlog.c:8362 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [25-1] :[] DEBUG: 00000: performing replication slot checkpoint Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [25-2] :[] LOCATION: CheckPointReplicationSlots, slot.c:1078 Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [26-1] :[] LOG: 00000: checkpoint complete: wrote 0 buffers (0.0%); 0 WALfile(s) added, 1 removed, 0 recycled; write=0.000 s, sync=0.000 s, total=0.007 s; sync files=0, longest=0.000 s, average=0.000s; distance=16272 kB, estimate=16272 kB Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [26-2] :[] LOCATION: LogCheckpointEnd, xlog.c:8435 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [27-1] :[] DEBUG: 00000: MultiXactId wrap limit is 2147483648, limitedby database with OID 1 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [27-2] :[] LOCATION: SetMultiXactIdLimit, multixact.c:2267 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [28-1] :[] DEBUG: 00000: MultiXact member stop limit is now 4294914944based on MultiXact 1 Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [28-2] :[] LOCATION: SetOffsetVacuumLimit, multixact.c:2630 There is no further information about anything concerning the logs, but at this point in time "FF" has disappeared. It was NOT copied out, we can see the timestamp on the pg_wal/archive_status still being at 17:09. Nothing except postgres is supposed to write/delete anything within the data tree, and the RedoLog.bck script doesn't delete anything at all. Another cute question would be: The "FE" log was successfully copied out at 17:09:45. The checkpoint at 17:09:55 then says "1 removed" - this should be the "FE", because the one before was written seven hours earlier (see the "ls" above) and should by long be gone. But then the checkpoint at 19:28:24 again says "1 removed". What was removed there? It is unlikely to be the "FE", and the "FF" would be currently in use - and the archive_status directory was not written since 17:09. But the "FF" has disappeared. So what is going on here? cheerio, PMc
On 6/8/20 5:02 PM, Peter wrote: > Hi all, > this is a 12.2 Release on FreeBSD 11.3. > > I am doing RedoLog Archiving according to Docs Chapter 25.1. There is no ReDo logging, there is WAL logging. What docs, because section 25.1 in the Postgres docs is : https://www.postgresql.org/docs/12/backup-dump.html 25.1. SQL Dump > > During the last week I have lost 4 distinct Redo Logs; they are > not in the backup. > > Loosing a RedoLog is very bad, because there is no redundancy, > loosing a single one of them makes the timeline disappear and it > will only reappear after another Base Backup. Very very bad. > > So I did analyze the matter. > > There are three ways to restart a Berkeley machine: > > 1. Cowboy it (aka pull-the-plug). This makes sure that everything is > certainly dead immediately, and, given all hard- and software is > well designed, nothing bad should happen. > > 2. Shut it down. This is the official means, and it takes very long, > because each and every applications are signalled and given time to > bring up whatever objections they may have. > > In this case "pg_ctl stop" will be invoked with whatever options the > sysop has configured, and postgres will copy out a full log into > archive before terminating. > > 3. Halt/Reboot it, like this: > https://www.freebsd.org/cgi/man.cgi?query=reboot&sektion=8&manpath=FreeBSD+11.3-RELEASE > This is considered more safe than pull-the-plug, and still fast. > Applications are killed without much waiting, but all disk buffers > are flushed to permanent storage and filesystems closed. > > In this case, it seems, Postgres will delete the current log > without archiving it. :( > > What precisely happens (according to the OS sources) during reboot > is this: processes will be sent SIGTERM, and after some 2-10 > seconds followed by SIGKILL. https://www.postgresql.org/docs/12/server-shutdown.html " Important It is best not to use SIGKILL to shut down the server. Doing so will prevent the server from releasing shared memory and semaphores. Furthermore, SIGKILL kills the postgres process without letting it relay the signal to its subprocesses, so it might be necessary to kill the individual subprocesses by hand as well. To terminate an individual session while allowing other sessions to continue, use pg_terminate_backend() (see Table 9.83) or send a SIGTERM signal to the child process associated with the session." What is RedoLog.bck? > > -------------------------------------- > > Lets have a closer look: > > We did a regular shutdown at 17:09, and then we did a reboot at 19:24. > > Here is the content of the staging area (where the logs are > copied to and accumulated until it is worth to run a backup job): > > # dir arch/ > total 240 > drwx------ 2 postgres postgres 5 Jun 8 17:09 . > drwxr-xr-x 6 postgres postgres 7 Jun 8 17:09 .. > -rw------- 1 postgres postgres 16777216 Jun 8 09:38 0000000100000017000000FC.ok > -rw------- 1 postgres postgres 16777216 Jun 8 10:48 0000000100000017000000FD.ok > -rw------- 1 postgres postgres 16777216 Jun 8 17:09 0000000100000017000000FE.ok > > And here is the pg_wal directory: > > # dir data12/pg_wal/ > total 89256 > drwx------ 3 postgres postgres 10 Jun 8 19:28 . > drwx------ 19 postgres postgres 23 Jun 8 19:28 .. > -rw------- 1 postgres postgres 335 Jun 7 07:36 0000000100000017000000EF.00000060.backup > -rw------- 1 postgres postgres 16777216 Jun 8 19:38 000000010000001800000000 > -rw------- 1 postgres postgres 16777216 Jun 7 07:17 000000010000001800000001 > -rw------- 1 postgres postgres 16777216 Jun 7 07:17 000000010000001800000002 > -rw------- 1 postgres postgres 16777216 Jun 7 07:17 000000010000001800000003 > -rw------- 1 postgres postgres 16777216 Jun 7 07:17 000000010000001800000004 > -rw------- 1 postgres postgres 16777216 Jun 7 07:36 000000010000001800000005 > drwx------ 2 postgres postgres 3 Jun 8 17:09 archive_status > # dir data12/pg_wal/archive_status > total 23 > drwx------ 2 postgres postgres 3 Jun 8 17:09 . > drwx------ 3 postgres postgres 10 Jun 8 19:28 .. > -rw------- 1 postgres postgres 0 Jun 7 07:36 0000000100000017000000EF.00000060.backup.done > > Now where the hell is my "FF" log ??? > > Lets check syslog - this was the full shutdown at 17:09: > > Jun 8 17:09:38 <local0.info> admn pg-bck[73534]: [10-1] :[] LOG: 00000: received fast shutdown request > Jun 8 17:09:38 <local0.info> admn pg-bck[73534]: [10-2] :[] LOCATION: pmdie, postmaster.c:2780 > Jun 8 17:09:38 <local0.info> admn pg-bck[73534]: [11-1] :[] LOG: 00000: aborting any active transactions > Jun 8 17:09:38 <local0.info> admn pg-bck[73534]: [11-2] :[] LOCATION: pmdie, postmaster.c:2813 > Jun 8 17:09:38 <local0.debug> admn pg-bck[73549]: [10-1] :[] DEBUG: 00000: logical replication launcher shutting down > Jun 8 17:09:38 <local0.debug> admn pg-bck[73549]: [10-2] :[] LOCATION: ProcessInterrupts, postgres.c:2981 > Jun 8 17:09:38 <local0.info> admn pg-bck[73534]: [12-1] :[] LOG: 00000: background worker "logical replication launcher"(PID 73549) exited with exit code 1 > Jun 8 17:09:38 <local0.info> admn pg-bck[73534]: [12-2] :[] LOCATION: LogChildExit, postmaster.c:3657 > Jun 8 17:09:38 <local0.info> admn pg-bck[73544]: [13-1] :[] LOG: 00000: shutting down > Jun 8 17:09:38 <local0.info> admn pg-bck[73544]: [13-2] :[] LOCATION: ShutdownXLOG, xlog.c:8321 > Jun 8 17:09:45 <local0.info> admn pg-bck[82223]: RedoLog.bck invoked pg_wal/0000000100000017000000FE 0000000100000017000000FE > Jun 8 17:09:45 <local0.info> admn pg-bck[82223]: RedoLog.bck pg_wal/0000000100000017000000FE 0000000100000017000000FEreturns 0 > Jun 8 17:09:45 <local0.debug> admn pg-bck[73547]: [8-1] :[] DEBUG: 00000: archived write-ahead log file "0000000100000017000000FE" > Jun 8 17:09:45 <local0.debug> admn pg-bck[73547]: [8-2] :[] LOCATION: pgarch_archiveXlog, pgarch.c:675 > Jun 8 17:09:55 <local0.info> admn pg-bck[73544]: [14-1] :[] LOG: 00000: checkpoint starting: shutdown immediate > Jun 8 17:09:55 <local0.info> admn pg-bck[73544]: [14-2] :[] LOCATION: LogCheckpointStart, xlog.c:8362 > Jun 8 17:09:55 <local0.debug> admn pg-bck[73544]: [15-1] :[] DEBUG: 00000: performing replication slot checkpoint > Jun 8 17:09:55 <local0.debug> admn pg-bck[73544]: [15-2] :[] LOCATION: CheckPointReplicationSlots, slot.c:1078 > Jun 8 17:09:55 <local0.info> admn pg-bck[73544]: [16-1] :[] LOG: 00000: checkpoint complete: wrote 0 buffers (0.0%);0 WAL file(s) added, 1 removed, 0 recycled; write=0.000 s, sync=0.000 s, total=10.131 s; sync files=0, longest=0.000s, average=0.000 s; distance=16383 kB, estimate=16383 kB > Jun 8 17:09:55 <local0.info> admn pg-bck[73544]: [16-2] :[] LOCATION: LogCheckpointEnd, xlog.c:8435 > Jun 8 17:09:55 <local0.info> admn pg-bck[73534]: [13-1] :[] LOG: 00000: database system is shut down > Jun 8 17:09:55 <local0.info> admn pg-bck[73534]: [13-2] :[] LOCATION: UnlinkLockFiles, miscinit.c:859 > > So, "FE" was copied out okay, and we have it in the staging area. > > And here is the relevant stuff from the following startup - here we > consequentially are within the "FF" log: > > Jun 8 17:15:38 <local0.info> admn pg-bck[6366]: [8-1] :[] LOG: 00000: database system was shut down at 2020-06-08 17:09:55CEST > Jun 8 17:15:38 <local0.info> admn pg-bck[6366]: [8-2] :[] LOCATION: StartupXLOG, xlog.c:6242 > Jun 8 17:15:38 <local0.debug> admn pg-bck[6366]: [9-1] :[] DEBUG: 00000: checkpoint record is at 17/FF000024 > Jun 8 17:15:38 <local0.debug> admn pg-bck[6366]: [9-2] :[] LOCATION: StartupXLOG, xlog.c:6532 > Jun 8 17:15:38 <local0.debug> admn pg-bck[6366]: [10-1] :[] DEBUG: 00000: redo record is at 17/FF000024; shutdown true > ---------------------------------------- > >>From the fast reboot @ 19:24 noting at all is logged. > > At the following startup, we see that we are still within the "FF" > log: > > Jun 8 19:28:24 <local0.debug> admn pg-bck[6465]: [1-1] :[] DEBUG: 00000: registering background worker "logical replicationlauncher" > Jun 8 19:28:24 <local0.debug> admn pg-bck[6465]: [1-2] :[] LOCATION: RegisterBackgroundWorker, bgworker.c:854 > Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [2-1] :[] LOG: 00000: starting PostgreSQL 12.2 on i386-portbld-freebsd11.3,compiled by gcc9 (FreeBSD Ports Collection) 9.3.0, 32-bit > Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [2-2] :[] LOCATION: PostmasterMain, postmaster.c:997 > Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [3-1] :[] LOG: 00000: listening on IPv4 address "0.0.0.0", port 5433 > Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [3-2] :[] LOCATION: StreamServerPort, pqcomm.c:590 > Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [4-1] :[] LOG: 00000: listening on Unix socket "/tmp/.s.PGSQL.5433" > Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [4-2] :[] LOCATION: StreamServerPort, pqcomm.c:585 > Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [5-1] :[] LOG: 00000: ending log output to stderr > Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [5-2] :[] HINT: Future log output will go to log destination "syslog". > Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [5-3] :[] LOCATION: PostmasterMain, postmaster.c:1297 > Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [6-1] :[] LOG: XX000: could not send test message on socket for statisticscollector: Permission denied > Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [6-2] :[] LOCATION: pgstat_init, pgstat.c:486 > Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [7-1] :[] LOG: 00000: trying another address for the statistics collector > Jun 8 19:28:24 <local0.info> admn pg-bck[6465]: [7-2] :[] LOCATION: pgstat_init, pgstat.c:418 > Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [8-1] :[] LOG: 00000: database system was interrupted; last known upat 2020-06-08 17:25:38 CEST > Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [8-2] :[] LOCATION: StartupXLOG, xlog.c:6267 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [9-1] :[] DEBUG: 00000: checkpoint record is at 17/FF01BFE8 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [9-2] :[] LOCATION: StartupXLOG, xlog.c:6532 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [10-1] :[] DEBUG: 00000: redo record is at 17/FF01BFB4; shutdown false > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [10-2] :[] LOCATION: StartupXLOG, xlog.c:6609 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [11-1] :[] DEBUG: 00000: next transaction ID: 18955154; next OID: 145913 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [11-2] :[] LOCATION: StartupXLOG, xlog.c:6613 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [12-1] :[] DEBUG: 00000: next MultiXactId: 1; next MultiXactOffset:0 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [12-2] :[] LOCATION: StartupXLOG, xlog.c:6617 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [13-1] :[] DEBUG: 00000: oldest unfrozen transaction ID: 479, in database13777 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [13-2] :[] LOCATION: StartupXLOG, xlog.c:6620 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [14-1] :[] DEBUG: 00000: oldest MultiXactId: 1, in database 1 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [14-2] :[] LOCATION: StartupXLOG, xlog.c:6623 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [15-1] :[] DEBUG: 00000: commit timestamp Xid oldest/newest: 0/0 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [15-2] :[] LOCATION: StartupXLOG, xlog.c:6626 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [16-1] :[] DEBUG: 00000: transaction ID wrap limit is 2147484126, limitedby database with OID 13777 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [16-2] :[] LOCATION: SetTransactionIdLimit, varsup.c:408 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [17-1] :[] DEBUG: 00000: MultiXactId wrap limit is 2147483648, limitedby database with OID 1 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [17-2] :[] LOCATION: SetMultiXactIdLimit, multixact.c:2267 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [18-1] :[] DEBUG: 00000: starting up replication slots > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [18-2] :[] LOCATION: StartupReplicationSlots, slot.c:1114 > Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [19-1] :[] LOG: 00000: database system was not properly shut down; automaticrecovery in progress > Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [19-2] :[] LOCATION: StartupXLOG, xlog.c:6764 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [20-1] :[] DEBUG: 00000: resetting unlogged relations: cleanup 1 init0 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [20-2] :[] LOCATION: ResetUnloggedRelations, reinit.c:55 > Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [21-1] :[] LOG: 00000: redo starts at 17/FF01BFB4 > Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [21-2] :[] LOCATION: StartupXLOG, xlog.c:7035 > Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [22-1] :[] LOG: 00000: redo done at 17/FF01C098 > Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [22-2] :[] LOCATION: StartupXLOG, xlog.c:7297 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [23-1] :[] DEBUG: 00000: resetting unlogged relations: cleanup 0 init1 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [23-2] :[] LOCATION: ResetUnloggedRelations, reinit.c:55 > Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [24-1] :[] LOG: 00000: checkpoint starting: end-of-recovery immediate > Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [24-2] :[] LOCATION: LogCheckpointStart, xlog.c:8362 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [25-1] :[] DEBUG: 00000: performing replication slot checkpoint > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [25-2] :[] LOCATION: CheckPointReplicationSlots, slot.c:1078 > Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [26-1] :[] LOG: 00000: checkpoint complete: wrote 0 buffers (0.0%); 0WAL file(s) added, 1 removed, 0 recycled; write=0.000 s, sync=0.000 s, total=0.007 s; sync files=0, longest=0.000 s, average=0.000s; distance=16272 kB, estimate=16272 kB > Jun 8 19:28:24 <local0.info> admn pg-bck[6467]: [26-2] :[] LOCATION: LogCheckpointEnd, xlog.c:8435 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [27-1] :[] DEBUG: 00000: MultiXactId wrap limit is 2147483648, limitedby database with OID 1 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [27-2] :[] LOCATION: SetMultiXactIdLimit, multixact.c:2267 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [28-1] :[] DEBUG: 00000: MultiXact member stop limit is now 4294914944based on MultiXact 1 > Jun 8 19:28:24 <local0.debug> admn pg-bck[6467]: [28-2] :[] LOCATION: SetOffsetVacuumLimit, multixact.c:2630 > > There is no further information about anything concerning the logs, > but at this point in time "FF" has disappeared. It was NOT copied out, > we can see the timestamp on the pg_wal/archive_status still being at > 17:09. > > Nothing except postgres is supposed to write/delete anything within > the data tree, and the RedoLog.bck script doesn't delete anything at all. > > Another cute question would be: The "FE" log was successfully copied > out at 17:09:45. The checkpoint at 17:09:55 then says "1 removed" - > this should be the "FE", because the one before was written seven > hours earlier (see the "ls" above) and should by long be gone. > > But then the checkpoint at 19:28:24 again says "1 removed". What was > removed there? It is unlikely to be the "FE", and the "FF" would be > currently in use - and the archive_status directory was not written > since 17:09. But the "FF" has disappeared. So what is going on here? > > cheerio, > PMc > > -- Adrian Klaver adrian.klaver@aklaver.com
On Mon, Jun 8, 2020 at 5:17 PM Peter <pmc@citylink.dinoex.sub.org> wrote: > Loosing a RedoLog is very bad, because there is no redundancy, > loosing a single one of them makes the timeline disappear and it > will only reappear after another Base Backup. Very very bad. > In this case, it seems, Postgres will delete the current log > without archiving it. :( I strongly suspect that you were hit by the bug fixed in commit 4e87c483. You should upgrade to Postgres 12.3 ASAP, to get that fix: "Avoid premature recycling of WAL segments during crash recovery (Jehan-Guillaume de Rorthais) WAL segments that become ready to be archived during crash recovery were potentially recycled without being archived." Sorry that you were affected by this bug -- it really sucks. -- Peter Geoghegan
On Mon, Jun 08, 2020 at 05:40:20PM -0700, Peter Geoghegan wrote: ! ! I strongly suspect that you were hit by the bug fixed in commit ! 4e87c483. You should upgrade to Postgres 12.3 ASAP, to get that fix: ! ! "Avoid premature recycling of WAL segments during crash recovery ! (Jehan-Guillaume de Rorthais) ! ! WAL segments that become ready to be archived during crash recovery ! were potentially recycled without being archived." Ahh, thank You so much; this is good news: if it is an already known bug, I can close all efforts, remove the debug-switches again, stuff the sources back into their box and relax. ;) I did a check if I would find something about lost archiving logs, but didn't - and then it is always possible that it's just a mistake of mine - as I know I do make mistakes. And now for the nitpicking part :) On Mon, Jun 08, 2020 at 05:35:40PM -0700, Adrian Klaver wrote: ! > I am doing RedoLog Archiving according to Docs Chapter 25.1. ! ! There is no ReDo logging, there is WAL logging. Yes I know - and i don't care. Technically they're no longer WAL when they're going to be archived. Their purpose then becomes to redo the transactions, and even the messages say so: ! > LOG: 00000: redo done at 17/FF01C098 ! What docs, because section 25.1 in the Postgres docs is : ! ! https://www.postgresql.org/docs/12/backup-dump.html ! ! 25.1. SQL Dump Ups, mistake of mine. Should be 25.3.1. ! https://www.postgresql.org/docs/12/server-shutdown.html ! " ! Important ! ! It is best not to use SIGKILL to shut down the server. Doing so will prevent ! the server from releasing shared memory and semaphores. Furthermore, SIGKILL ! kills the postgres process without letting it relay the signal to its ! subprocesses, so it might be necessary to kill the individual subprocesses ! by hand as well. And which of these would be of any concern if the machine is rebooted anyway? I had to install new hardware, and currently I'm trying to identify a memory exhaustion issue. This makes it necessary to reboot the full system quite often, and I neither want to wait for orderly termination of dozens of subsytems, nor do I want to need fsck at restart. This would make SIGKILL/reboot the method of choice. ! What is RedoLog.bck? The script which one has to write according to the docs' section which would be correctly numbered 25.3.1. cheerio, PMc
On 6/8/20 6:38 PM, Peter wrote: > On Mon, Jun 08, 2020 at 05:40:20PM -0700, Peter Geoghegan wrote: > > And now for the nitpicking part :) > > On Mon, Jun 08, 2020 at 05:35:40PM -0700, Adrian Klaver wrote: > > ! > I am doing RedoLog Archiving according to Docs Chapter 25.1. > ! > ! There is no ReDo logging, there is WAL logging. > > Yes I know - and i don't care. Technically they're no longer WAL when > they're going to be archived. Their purpose then becomes to redo the Not according to the section you are referring to: 25.3.1. Setting Up WAL Archiving Redoing is the process of replaying the WAL logs. > Ups, mistake of mine. Should be 25.3.1. > > And which of these would be of any concern if the machine is rebooted > anyway? > > I had to install new hardware, and currently I'm trying to identify > a memory exhaustion issue. This makes it necessary to reboot the full > system quite often, and I neither want to wait for orderly termination > of dozens of subsytems, nor do I want to need fsck at restart. This > would make SIGKILL/reboot the method of choice. That is your prerogative, just not sure it is conducive to the health of your system. > > ! What is RedoLog.bck? > > The script which one has to write according to the docs' section which > would be correctly numbered 25.3.1. > > cheerio, > PMc > > -- Adrian Klaver adrian.klaver@aklaver.com
Actually, the affair had some good side: as usual I was checking
my own designs first and looking for flaws, and indeed I found one:
If you do copy out the archive logs not directly to tape, but to
some disk area for further processing, then there is an issue with
possible loss. If you do it like the docs say, with a command like
this:
archive_command = 'test ! -f /mnt/server/archivedir/%f && cp %p
+/mnt/server/archivedir/%f' # Unix
That "cp" is usually not synchronous. So there is the possibility
that this command terminates successfully, and reports exitcode zero
back to the Postgres, and then the Postgres will consider that log
being safely away.
But the target of the copy may not yet been written to disk. If
at that point a power loss happens, the log may become missing/damaged/
incomplete, while the database may or may not consider it done
when restarting.
Therefore, mounting such a target filesystem in all-synchronous mode
might be a good idea. (UFS: "-o sync", ZFS: "set sync=always")
cheerio,
PMc
On 6/8/20 7:33 PM, Peter wrote: > > Actually, the affair had some good side: as usual I was checking > my own designs first and looking for flaws, and indeed I found one: > > If you do copy out the archive logs not directly to tape, but to > some disk area for further processing, then there is an issue with > possible loss. If you do it like the docs say, with a command like > this: > > archive_command = 'test ! -f /mnt/server/archivedir/%f && cp %p > +/mnt/server/archivedir/%f' # Unix > > That "cp" is usually not synchronous. So there is the possibility > that this command terminates successfully, and reports exitcode zero > back to the Postgres, and then the Postgres will consider that log > being safely away. Which is why just following the above command in the docs is: "(This is an example, not a recommendation, and might not work on all platforms.) " Generally for peace of mind folks use third party tools like: pg_backrest(https://pgbackrest.org/), pg_probackup(https://postgrespro.com/products/extensions/pg_probackup) or Barman(https://www.pgbarman.org/). as they offer safety checks for your backups. I use pg_backrest, but it does not look promising for running on BSD: https://fluca1978.github.io/2019/03/04/pgbackrest_FreeBSD.html Not sure about pg_probackup. Barman is Python package: http://docs.pgbarman.org/release/2.10/#installation-from-sources > > But the target of the copy may not yet been written to disk. If > at that point a power loss happens, the log may become missing/damaged/ > incomplete, while the database may or may not consider it done > when restarting. > > Therefore, mounting such a target filesystem in all-synchronous mode > might be a good idea. (UFS: "-o sync", ZFS: "set sync=always") > > cheerio, > PMc > > -- Adrian Klaver adrian.klaver@aklaver.com
Adrian Klaver <adrian.klaver@aklaver.com> writes:
> On 6/8/20 7:33 PM, Peter wrote:
>> That "cp" is usually not synchronous. So there is the possibility
>> that this command terminates successfully, and reports exitcode zero
>> back to the Postgres, and then the Postgres will consider that log
>> being safely away.
> Which is why just following the above command in the docs is:
> "(This is an example, not a recommendation, and might not work on all
> platforms.) "
Yeah. There have been discussions about changing that disclaimer to be
more forceful, because in point of fact a plain "cp" is generally not safe
enough. You need to fsync the written file, and on many filesystems you
also have to fsync the directory it's in.
> Generally for peace of mind folks use third party tools like:
+1. Rolling your own archive script is seldom advisable.
regards, tom lane
Greetings, * Adrian Klaver (adrian.klaver@aklaver.com) wrote: > I use pg_backrest, but it does not look promising for running on BSD: > https://fluca1978.github.io/2019/03/04/pgbackrest_FreeBSD.html That's an unfortunately ancient post, really, considering that pgbackrest has now been fully rewritten into C, and Luca as recently as September 2019 was saying he has it working on FreeBSD. If folks do run into issues with pgbackrest on FreeBSD, please let us know. Thanks, Stephen
Вложения
On 6/9/20 4:15 AM, Stephen Frost wrote: > Greetings, > > * Adrian Klaver (adrian.klaver@aklaver.com) wrote: >> I use pg_backrest, but it does not look promising for running on BSD: >> https://fluca1978.github.io/2019/03/04/pgbackrest_FreeBSD.html > > That's an unfortunately ancient post, really, considering that > pgbackrest has now been fully rewritten into C, and Luca as recently as > September 2019 was saying he has it working on FreeBSD. Yeah, but this: https://github.com/pgbackrest/pgbackrest/issues/686 is not clear on whether a user can do that w/o a certain amount of hand holding. > > If folks do run into issues with pgbackrest on FreeBSD, please let us > know. > > Thanks, > > Stephen > -- Adrian Klaver adrian.klaver@aklaver.com
Greetings, * Adrian Klaver (adrian.klaver@aklaver.com) wrote: > On 6/9/20 4:15 AM, Stephen Frost wrote: > >* Adrian Klaver (adrian.klaver@aklaver.com) wrote: > >>I use pg_backrest, but it does not look promising for running on BSD: > >>https://fluca1978.github.io/2019/03/04/pgbackrest_FreeBSD.html > > > >That's an unfortunately ancient post, really, considering that > >pgbackrest has now been fully rewritten into C, and Luca as recently as > >September 2019 was saying he has it working on FreeBSD. > > Yeah, but this: > > https://github.com/pgbackrest/pgbackrest/issues/686 > > is not clear on whether a user can do that w/o a certain amount of hand > holding. I've asked Luca to update his blog post and/or re-test on FreeBSD and he's said he would. We've moved to using autoconf and friends, and it's all in C now, so it really shouldn't be as much of an issue these days. I recall someone else building on FreeBSD not long ago, but not finding a reference to it offhand. > >If folks do run into issues with pgbackrest on FreeBSD, please let us > >know. ... again, this. Thanks, Stephen
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On Mon, Jun 08, 2020 at 09:21:47PM -0700, Adrian Klaver wrote: ! ! On 6/8/20 7:33 PM, Peter wrote: ! > ! > Actually, the affair had some good side: as usual I was checking ! > my own designs first and looking for flaws, and indeed I found one: ! > If you do copy out the archive logs not directly to tape, but to ! > some disk area for further processing, then there is an issue with ! > possible loss. If you do it like the docs say, with a command like ! > this: ! > archive_command = 'test ! -f /mnt/server/archivedir/%f && cp %p ! > +/mnt/server/archivedir/%f' # Unix ! > That "cp" is usually not synchronous. So there is the possibility ! > that this command terminates successfully, and reports exitcode zero ! > back to the Postgres, and then the Postgres will consider that log ! > being safely away. ! ! Which is why just following the above command in the docs is: ! ! "(This is an example, not a recommendation, and might not work on all ! platforms.) " So, what You are basically saying is: my worries are justified and correctly founded, and this is indeed a matter that needs to be taken care of. Thank You. ! Generally for peace of mind folks use third party tools like: ! ! pg_backrest(https://pgbackrest.org/), ! pg_probackup(https://postgrespro.com/products/extensions/pg_probackup) or ! Barman(https://www.pgbarman.org/). Hmja. We may on occasion have a look into these... ! I use pg_backrest, but it does not look promising for running on BSD: ! https://fluca1978.github.io/2019/03/04/pgbackrest_FreeBSD.html That looks mostly like the usual things which can be fixed. Now, for the facts: I am already using a professional backup solution. (It is actually a "dual-use/commercial" solution, of the kind which you can either fetch from github and use without support, or buy with a contract or whatever and get support.) With this professional backup solution I have already identified 28 (spell: twenty-eight) bugs, and fixed/workarounded these, until I got it properly working. This professional backup solution also offers support for postgres. Sadly, it only covers postgres up to Rel.9, and that piece of software wasn't touched in the last 6 or 7 years. But the bigger issue there is, that backup solution needs it's own postgres database as it's backend - and it cannot backup the database it is using. Looks quite pointless to me, then. So I just did it all with shell (and it wasn't many lines). So now, as I've been thru identifying and handling all the issues in that one backup solution, and since it is supposed to handle *all* backup demands (and not only postgres), I will certainly not start and go thru the same process again with one of these supposed solutions, where 90% of the code tries to solve the same things redundantly again, but then only for PG. Actually, I am getting very tired of reading that something which can easily be done within 20 lines of shell scripting, would need special "solutions", solutions that need to be compiled, solutions that would bring along their own fashion of interpreter, solutions that have a lot of their own dependencies and introduce mainly one thing: new bugs. Does nobody know anymore how to do proper systems management scripting? Using just the basic system tools which have proven to work for more than 50 years now!? ! Not sure about pg_probackup. Okay, I had a -very short- look into these. Just scanning the introductory pages. The only really interesting thing there is the pg_probackup. These folks seem to have found a way to do row-level incremental backups. And pgbarman seems to have an impressive understanding of ITIL (in case anybody bothers about that). All these tools do only cover PG, but do that in any possible regards. This is fine as long as you do not run any computers, and the only application you are using is Postgres. But, if you have other applications as well, or have computers, then you will need a different backup solution, something that will cover your site-wide backup demands, in a consistent fashion (think something in the style of ADSM, or nowadays called Spectrum Protect). And then 90% of the things offered here become superfluous, because they are already handled site-wide. And then you will have to consider integration of both pieces - and that will most likely be more work and more error-prone than just writing a few adapters in shell. cheerio, PMc
On Tue, Jun 09, 2020 at 01:27:20AM -0400, Tom Lane wrote: ! Adrian Klaver <adrian.klaver@aklaver.com> writes: ! > On 6/8/20 7:33 PM, Peter wrote: ! >> That "cp" is usually not synchronous. So there is the possibility ! >> that this command terminates successfully, and reports exitcode zero ! >> back to the Postgres, and then the Postgres will consider that log ! >> being safely away. ! ! > Which is why just following the above command in the docs is: ! > "(This is an example, not a recommendation, and might not work on all ! > platforms.) " ! ! Yeah. There have been discussions about changing that disclaimer to be ! more forceful, because in point of fact a plain "cp" is generally not safe ! enough. You need to fsync the written file, and on many filesystems you ! also have to fsync the directory it's in. It certainly does not need to be "more forceful" - because this is not about behavioural education, like training dogs, horses, or monkeys, and neither do we entertain a BDSM studio. What it needs instead is mention of the magic word "fsync". Because, we already know that - we just need a reminder at the proper place. Systems integrators are professional people. They are not in need of more beating (spell: forceful education), only of substantial technical hints and informations. ! > Generally for peace of mind folks use third party tools like: ! ! +1. Rolling your own archive script is seldom advisable. Well then, using commercial solutions brings it's own problems. E.g., the people I happened to work for often had problems with torsion, which happens when the solution gets longer than, say, twenty meters, and these are walked at high speeds. They didn't have a problem with scripting - rather the opposite, they were happy with it and paid good money for. cheerio, PMc
On 6/9/20 10:55 AM, Peter wrote: > On Mon, Jun 08, 2020 at 09:21:47PM -0700, Adrian Klaver wrote: > ! > ! On 6/8/20 7:33 PM, Peter wrote: > ! > > ! > Actually, the affair had some good side: as usual I was checking > ! > my own designs first and looking for flaws, and indeed I found one: > ! > If you do copy out the archive logs not directly to tape, but to > ! > some disk area for further processing, then there is an issue with > ! > possible loss. If you do it like the docs say, with a command like > ! > this: > ! > archive_command = 'test ! -f /mnt/server/archivedir/%f && cp %p > ! > +/mnt/server/archivedir/%f' # Unix > ! > That "cp" is usually not synchronous. So there is the possibility > ! > that this command terminates successfully, and reports exitcode zero > ! > back to the Postgres, and then the Postgres will consider that log > ! > being safely away. > ! > ! Which is why just following the above command in the docs is: > ! > ! "(This is an example, not a recommendation, and might not work on all > ! platforms.) " > > So, what You are basically saying is: my worries are justified and > correctly founded, and this is indeed a matter that needs to be taken > care of. > Thank You. > > ! Generally for peace of mind folks use third party tools like: > ! > ! pg_backrest(https://pgbackrest.org/), > ! pg_probackup(https://postgrespro.com/products/extensions/pg_probackup) or > ! Barman(https://www.pgbarman.org/). > > Hmja. We may on occasion have a look into these... > > ! I use pg_backrest, but it does not look promising for running on BSD: > ! https://fluca1978.github.io/2019/03/04/pgbackrest_FreeBSD.html > > That looks mostly like the usual things which can be fixed. > > Now, for the facts: I am already using a professional backup > solution. (It is actually a "dual-use/commercial" solution, of the > kind which you can either fetch from github and use without support, > or buy with a contract or whatever and get support.) > > With this professional backup solution I have already identified 28 > (spell: twenty-eight) bugs, and fixed/workarounded these, until I got it > properly working. > > This professional backup solution also offers support for postgres. > Sadly, it only covers postgres up to Rel.9, and that piece of software > wasn't touched in the last 6 or 7 years. > But the bigger issue there is, that backup solution needs it's > own postgres database as it's backend - and it cannot backup the > database it is using. Looks quite pointless to me, then. > So I just did it all with shell (and it wasn't many lines). The backup solution is? > > So now, as I've been thru identifying and handling all the issues in > that one backup solution, and since it is supposed to handle *all* > backup demands (and not only postgres), I will certainly not start > and go thru the same process again with one of these supposed > solutions, where 90% of the code tries to solve the same things > redundantly again, but then only for PG. They are not supposed. They are in use by many people/organizations across a wide variety of installations. > > > Actually, I am getting very tired of reading that something which can > easily be done within 20 lines of shell scripting, would need special > "solutions", solutions that need to be compiled, solutions that would > bring along their own fashion of interpreter, solutions that have a > lot of their own dependencies and introduce mainly one thing: new bugs. They where developed as they could not be done in 20 lines of shell scripting and work at a reliable level. Fine rant below. Go forth and work your wonders. > > Does nobody know anymore how to do proper systems management > scripting? Using just the basic system tools which have proven to > work for more than 50 years now!? > > ! Not sure about pg_probackup. > > Okay, I had a -very short- look into these. Just scanning the > introductory pages. > > The only really interesting thing there is the pg_probackup. These > folks seem to have found a way to do row-level incremental backups. > > And pgbarman seems to have an impressive understanding of ITIL (in > case anybody bothers about that). > > All these tools do only cover PG, but do that in any possible regards. > > This is fine as long as you do not run any computers, and the only > application you are using is Postgres. > But, if you have other applications as well, or have computers, then > you will need a different backup solution, something that will cover > your site-wide backup demands, in a consistent fashion (think > something in the style of ADSM, or nowadays called Spectrum Protect). > > And then 90% of the things offered here become superfluous, because > they are already handled site-wide. And then you will have to > consider integration of both pieces - and that will most likely be > more work and more error-prone than just writing a few adapters in > shell. > > > > cheerio, > PMc > -- Adrian Klaver adrian.klaver@aklaver.com
Greetings, * Peter (pmc@citylink.dinoex.sub.org) wrote: > This professional backup solution also offers support for postgres. > Sadly, it only covers postgres up to Rel.9, and that piece of software > wasn't touched in the last 6 or 7 years. Then it certainly doesn't work with the changes in v12, and probably has other issues, as you allude to. > Actually, I am getting very tired of reading that something which can > easily be done within 20 lines of shell scripting, would need special This is just simply false- you can't do it properly in 20 lines of shell scripting. Sure, you can write something that has probably next to no error checking, uses the deprecated API that'll cause your systems to fail to start if you ever happen to have a reboot during a backup, and has no way to provide verification that the backup was at all successful after the fact, but that's not what I'd consider a proper solution- instead it's one that'll end up causing you a lot of pain down the road. Even the shell-script based solution (which I've never used and personally wouldn't really recommend, but to each their own) called 'pitery' (available here: https://github.com/dalibo/pitrery) is thousands of lines of code. > Does nobody know anymore how to do proper systems management > scripting? Using just the basic system tools which have proven to > work for more than 50 years now!? I've not met anything I'd call 'proper systems management scripting' that's 20 lines of code, shell script or not. > ! Not sure about pg_probackup. > > Okay, I had a -very short- look into these. Just scanning the > introductory pages. > > The only really interesting thing there is the pg_probackup. These > folks seem to have found a way to do row-level incremental backups. pg_probackup doesn't do row-level incremental backups, unless I've missed some pretty serious change in its development, but it does provide page-level, with, as I recall, an extension that didn't get good reception when it was posted and discussed on these mailing lists by other PG hackers. I don't know if those concerns about it have been addressed or not, you might ask the pg_probackup folks if you're considering it as a solution. > This is fine as long as you do not run any computers, and the only > application you are using is Postgres. > But, if you have other applications as well, or have computers, then > you will need a different backup solution, something that will cover > your site-wide backup demands, in a consistent fashion (think > something in the style of ADSM, or nowadays called Spectrum Protect). > > And then 90% of the things offered here become superfluous, because > they are already handled site-wide. And then you will have to > consider integration of both pieces - and that will most likely be > more work and more error-prone than just writing a few adapters in > shell. pgbackrest's repo can be safely backed up using the simple file-based backup utilities that you're referring to here. I suspect some of the other solution's backups also could be, but you'd probably want to make sure. PG generally isn't something that can be backed up using the simple file based backup solutions, as you might appreciate from just considering the number of tools written to specifically deal with the complexity of backing up an online PG cluster. Thanks, Stephen
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On 6/9/20 12:02 PM, Peter wrote: > On Tue, Jun 09, 2020 at 01:27:20AM -0400, Tom Lane wrote: > ! Adrian Klaver <adrian.klaver@aklaver.com> writes: > ! > On 6/8/20 7:33 PM, Peter wrote: > ! >> That "cp" is usually not synchronous. So there is the possibility > ! >> that this command terminates successfully, and reports exitcode zero > ! >> back to the Postgres, and then the Postgres will consider that log > ! >> being safely away. > ! > ! > Which is why just following the above command in the docs is: > ! > "(This is an example, not a recommendation, and might not work on all > ! > platforms.) " > ! > ! Yeah. There have been discussions about changing that disclaimer to be > ! more forceful, because in point of fact a plain "cp" is generally not safe > ! enough. You need to fsync the written file, and on many filesystems you > ! also have to fsync the directory it's in. > > It certainly does not need to be "more forceful" - because this is not > about behavioural education, like training dogs, horses, or monkeys, > and neither do we entertain a BDSM studio. > > What it needs instead is mention of the magic word "fsync". Because, > we already know that - we just need a reminder at the proper place. > > Systems integrators are professional people. They are not in need of > more beating (spell: forceful education), only of substantial > technical hints and informations. > > ! > Generally for peace of mind folks use third party tools like: > ! > ! +1. Rolling your own archive script is seldom advisable. > > Well then, using commercial solutions brings it's own problems. E.g., FYI, the projects Stephen and I mentioned are Open Source. I'm sure you can get paid support for them, but you exist a higher plane then that so you can use then for free. > the people I happened to work for often had problems with torsion, > which happens when the solution gets longer than, say, twenty meters, > and these are walked at high speeds. > > They didn't have a problem with scripting - rather the opposite, they > were happy with it and paid good money for. > > > cheerio, > PMc > -- Adrian Klaver adrian.klaver@aklaver.com
On Tue, Jun 09, 2020 at 12:34:38PM -0700, Adrian Klaver wrote: ! The backup solution is? https://www.bareos.com/ ! Fine rant below. Go forth and work your wonders. I don't need to, anymore. I did that, for about 20 years - people I used to work for as a consultant (major banks and insurance shops) would usually run Informix or Oracle. Postgres is just my own private fancy. On Tue, Jun 09, 2020 at 03:42:48PM -0400, Stephen Frost wrote: ! * Peter (pmc@citylink.dinoex.sub.org) wrote: ! > This professional backup solution also offers support for postgres. ! > Sadly, it only covers postgres up to Rel.9, and that piece of software ! > wasn't touched in the last 6 or 7 years. ! ! Then it certainly doesn't work with the changes in v12, and probably has ! other issues, as you allude to. Just having a look at their webpage, something seems to have been updated recently, they now state that they have a new postgres adapter: https://www.bareos.com/en/company_news/postgres-plugin-en1.html Enjoy reading, and tell us what You think. ! > Actually, I am getting very tired of reading that something which can ! > easily be done within 20 lines of shell scripting, would need special ! ! This is just simply false- you can't do it properly in 20 lines of shell ! scripting. Well, Your own docs show how to do it with a one-liner. So please don't blame me for improving that to 20 lines. ! Sure, you can write something that has probably next to no ! error checking, Before judging that, one should first specify what precisely is the demand. In a basic approach, the demand may be to get the logs out on tape in a failsafe automated fashion without any miss, and get the data tree out periodically, and have guaranteed that these files are untampered as on disk. And that can very well be done properly with an incremental filesystem backup software plus some 20 lines of shellscript. Now talking about doing an automated restore, or, having some menu- driven solution, or -the worst of all- having a solution that can be operated by morons - that's an entirely different matter. In my understanding, backup is done via pgdump. The archive logs are for emergencies (data corruption, desaster), only. And emergencies would usually be handled by some professional people who know what they have to do. You may consider different demands, and that is also fine, but doesn't need to concern me. ! uses the deprecated API that'll cause your systems to ! fail to start if you ever happen to have a reboot during a backup It is highly unlikely that I did never have that happen during 15 years. So what does that mean? If I throw in a pg_start_backup('bogus'), and then restart the cluster, it will not work anymore? Lets see... Clean stop/start - no issue whatsoever. (LOG: online backup mode canceled) kill -9 the whole flock - no issue whatsoever (Log: database system was interrupted) I won't pull the plug now, but that has certainly happened lots of times in the past, and also yielded no issue whatsoever - simply because there *never* was *any* issue whatsover with Postgres (until I got the idea to install the relatively fresh R.12 - but that's understandable). So maybe this problem exists only on Windows? And yes, I read that whole horrible discussion, and I could tear my hair out, really, concerning the "deprecated API". I suppose You mean the mentioning in the docs that the "exclusive low-level backup" is somehow deprecated. This is a very big bad. Because: normally you can run the base backup as a strictly ordinary file-level backup in "full" mode, just as any backup software can do it. You will simply execute the pg_start_backup() and pg_stop_backup() commands in the before- and after- hooks - and any backup software will offer these hooks. But now, with the now recommended "non-exclusive low-level backup", the task is different: now your before-hook needs to do two things at the same time: 1. keep a socket open in order to hold the connection to postgres (because postgres will terminate the backup when the socket is closed), and 2. invoke exit(0) (because the actual backup will not start until the before- hook has properly delivered a successful exit code. And, that is not only difficult, it is impossible. So, what has to be done instead: you need to write a separate network daemon, with the only purpose of holding that connection to postgres open. And that network daemon needs to handle the communication to the backup software on one side, and to postgres on the other side. And that network daemon then needs the full-blown feature requirements as a fail-safe network daemon should have (and that is a LOT!), plus it needs to handle all kinds of possible failures (like network interruptions) in that triangle, during the backup, and properly notify both sides of whatever might be ongoing (and that is NOT trivial). So yes, this is really a LOT of work. But the point is: this all is not really necessary, because currently the stuff works fine in the old way. So, well, do away with the old method - but you cannot do it away inside of rel.12 - and then I will stay with 12 for as long as possible (and I don't think I will be the only one). ! has no way to provide verification that the backup was at all successful It doesn't need to. Thats the main point of using file level standard backup - if that is tested and works, then it works for the data tree and the logs just the same. And any monitoring is also just the same. I see no point in creating artificial complications, which then create a necessity for individual tools to handle them, which then create a new requirement for testing and validating all these individual tools - as this is strictly against the original idea as Brian Kernighan explained it: use simple and versatile tools, and combine these to achieve the individual task. ! > The only really interesting thing there is the pg_probackup. These ! > folks seem to have found a way to do row-level incremental backups. ! ! pg_probackup doesn't do row-level incremental backups, unless I've ! missed some pretty serious change in its development, but it does ! provide page-level, Ah, well, anyway that seems to be something significantly smaller than the usual 1 gig table file at once. ! with, as I recall, an extension that didn't get ! good reception when it was posted and discussed on these mailing lists ! by other PG hackers. I don't know if those concerns about it have been ! addressed or not, you might ask the pg_probackup folks if you're ! considering it as a solution. Okay, thanks. That's interesting. I was just thinking if one could cannibalize that respective code and make it into a filter for my own purposes. And yes, the license would allow that. And I was thinking that it will be quite an effort to get some kind of logical verification that this scheme does actually work properly. I don't consider it as a solution; I consider it as a piece of functionality that, if working properly, does actually increase the possibilities. ! PG generally isn't something that can be backed up using the simple file ! based backup solutions, as you might appreciate from just considering ! the number of tools written to specifically deal with the complexity of ! backing up an online PG cluster. Yes, one could assume that. But then, I would prefer well-founded technical reasons for what exactly would not work that way, and why it would not work that way. And there seems to be not much about that. And in such a case I tend to trust my own understanding, similar to the full_page_writes matter. (In 2008 I heard about ZFS, and I concluded that if ZFS is indeed copy-on-write, and if the description of the full_page_writes option is correct, then one could safely switch it off and free a lot of backup space - factor 10 at that time, with some Rel.8. And so I started to use ZFS. Nobody would confirm that at that time, but nowadays everybody does it.) This was actually my job as a consultant: to de-mystify technology, and make it understandable as an arrangement of well explainable pieces of functionality with well-deducible consequences. But this is no longer respected today; now people are expected to *NOT* understand the technology they handle, and instead believe in marketing and that it all is very complicated and un-intellegible. cheerio, PMc
Greetings, * Peter (pmc@citylink.dinoex.sub.org) wrote: > On Tue, Jun 09, 2020 at 03:42:48PM -0400, Stephen Frost wrote: > ! * Peter (pmc@citylink.dinoex.sub.org) wrote: > ! > This professional backup solution also offers support for postgres. > ! > Sadly, it only covers postgres up to Rel.9, and that piece of software > ! > wasn't touched in the last 6 or 7 years. > ! > ! Then it certainly doesn't work with the changes in v12, and probably has > ! other issues, as you allude to. > > Just having a look at their webpage, something seems to have been updated > recently, they now state that they have a new postgres adapter: > > https://www.bareos.com/en/company_news/postgres-plugin-en1.html > Enjoy reading, and tell us what You think. I'm afraid I'm not particularly interested in performing a pro bono evaluation of a commercial product, though considering they've put out a press release with obviously broken links, I already have suspicions of what I'd find ... (try clicking on their 'experimental/nightly' link). A quick look at the docs also shows that it's referring to recovery.conf, which no longer exists since v12 was released back in September, so, yeah, isn't exactly current. > ! > Actually, I am getting very tired of reading that something which can > ! > easily be done within 20 lines of shell scripting, would need special > ! > ! This is just simply false- you can't do it properly in 20 lines of shell > ! scripting. > > Well, Your own docs show how to do it with a one-liner. So please > don't blame me for improving that to 20 lines. No, the documentation provides an example for the purpose of understanding how the replacement in the command is done and explicitly says that you probably shouldn't use that command. > ! Sure, you can write something that has probably next to no > ! error checking, > > Before judging that, one should first specify what precisely is the > demand. I really don't need to in order to be able to judge the notion of a 20 line shell script being able to manage to perform a backup correctly. > In my understanding, backup is done via pgdump. The archive logs are > for emergencies (data corruption, desaster), only. And emergencies > would usually be handled by some professional people who know what > they have to do. No, that's not the case. pg_dump isn't at all involved in the backups that we're talking about here which are physical, file-level, backups. > ! uses the deprecated API that'll cause your systems to > ! fail to start if you ever happen to have a reboot during a backup > > It is highly unlikely that I did never have that happen during 15 > years. So what does that mean? If I throw in a pg_start_backup('bogus'), > and then restart the cluster, it will not work anymore? If you perform a pg_start_backup(), have a checkpoint happen such that older WAL is removed, and then reboot the box or kill -9 postgres, no, it's not going to start anymore because there's going to be a backup_label file that is telling the cluster that it needs to start replaying WAL from an older point in time than what you've got WAL for. > Lets see... > Clean stop/start - no issue whatsoever. (LOG: online backup mode > canceled) > kill -9 the whole flock - no issue whatsoever (Log: database system > was interrupted) > I won't pull the plug now, but that has certainly happened lots of > times in the past, and also yielded no issue whatsoever - simply > because there *never* was *any* issue whatsover with Postgres (until > I got the idea to install the relatively fresh R.12 - but that's > understandable). Being lucky really isn't what you want to bet on. > So maybe this problem exists only on Windows? No, it's not Windows specific. > And yes, I read that whole horrible discussion, and I could tear my > hair out, really, concerning the "deprecated API". I suppose You mean > the mentioning in the docs that the "exclusive low-level backup" is > somehow deprecated. Yes, it's deprecated specifically because of the issues outlined above. They aren't hypothetical, they do happen, and people do get bit by them. > This is a very big bad. Because: normally you can run the base backup > as a strictly ordinary file-level backup in "full" mode, just as any > backup software can do it. You will simply execute the > pg_start_backup() and pg_stop_backup() commands in the before- and > after- hooks - and any backup software will offer these hooks. > > But now, with the now recommended "non-exclusive low-level backup", > the task is different: now your before-hook needs to do two things > at the same time: > 1. keep a socket open in order to hold the connection to postgres > (because postgres will terminate the backup when the socket is > closed), and > 2. invoke exit(0) (because the actual backup will not start until > the before- hook has properly delivered a successful exit code. > And, that is not only difficult, it is impossible. One would imagine that if the commercial vendors wished to actually support PG properly, they'd manage to figure out a way to do so that doesn't involve the kind of hook scripts and poor assumptions made about them that you're discussing here. Considering that every single backup solution written specifically for PG, including the shell-based ones, have managed to figure out how to work with the new API, it hardly seems impossible for them to do so. > So yes, this is really a LOT of work. But the point is: this all is > not really necessary, because currently the stuff works fine in the > old way. Unfortunately, no, it doesn't work fine in the general case- you might be lucky enough to get it to work sometimes without failure, but that's not how one designs systems, to work in the 'lucky' case and fail badly in other cases. > So, well, do away with the old method - but you cannot do it away > inside of rel.12 - and then I will stay with 12 for as long as > possible (and I don't think I will be the only one). You're welcome to stay with it as long as you'd like. I do hope we finally rip it out, as was discussed before, in v13. Of course, we'll stop supporting v12 about 5 years after we release it. > I see no point in creating artificial complications, which then create > a necessity for individual tools to handle them, which then create a > new requirement for testing and validating all these individual tools - > as this is strictly against the original idea as Brian Kernighan > explained it: use simple and versatile tools, and combine these to > achieve the individual task. These aren't artificial complications. > ! PG generally isn't something that can be backed up using the simple file > ! based backup solutions, as you might appreciate from just considering > ! the number of tools written to specifically deal with the complexity of > ! backing up an online PG cluster. > > Yes, one could assume that. But then, I would prefer well-founded > technical reasons for what exactly would not work that way, and why it > would not work that way. And there seems to be not much about that. I've explained them above, and they were explained on the thread you evidently glanced at regarding deprecating the old API. > And in such a case I tend to trust my own understanding, similar to the > full_page_writes matter. (In 2008 I heard about ZFS, and I concluded > that if ZFS is indeed copy-on-write, and if the description of the > full_page_writes option is correct, then one could safely switch it > off and free a lot of backup space - factor 10 at that time, with some > Rel.8. And so I started to use ZFS. Nobody would confirm that at that > time, but nowadays everybody does it.) I don't agree that 'everybody does it', nor that it's a particularly good idea to turn off full_page_writes and depend on ZFS to magic it. In fact, I'd suggest you go watch this PGCon talk, once it's available later this month (from a competitor of mine, but a terribly smart individual, so you don't need to listen to me about it)- https://www.pgcon.org/events/pgcon_2020/schedule/session/101-avoiding-detecting-and-recovering-from-data-corruption/ > This was actually my job as a consultant: to de-mystify technology, > and make it understandable as an arrangement of well explainable > pieces of functionality with well-deducible consequences. > But this is no longer respected today; now people are expected to > *NOT* understand the technology they handle, and instead believe > in marketing and that it all is very complicated and un-intellegible. Perhaps I'm wrong, but I tend to feel like I've got a pretty decent handle on both PostgreSQL and on how file-level backups of it work. Thanks, Stephen
Вложения
On 6/9/20 4:35 PM, Peter wrote: > On Tue, Jun 09, 2020 at 12:34:38PM -0700, Adrian Klaver wrote: > > > And that can very well be done properly with an incremental filesystem > backup software plus some 20 lines of shellscript. Read the caveats here: https://www.postgresql.org/docs/12/backup-file.html > > Now talking about doing an automated restore, or, having some menu- > driven solution, or -the worst of all- having a solution that can be > operated by morons - that's an entirely different matter. > > In my understanding, backup is done via pgdump. The archive logs are > for emergencies (data corruption, desaster), only. And emergencies > would usually be handled by some professional people who know what > they have to do. Read the entire section below, for why WAL's are for backup also. FYI, if you don't properly set it up then you may not be protected for data corruption. See PITR. https://www.postgresql.org/docs/12/continuous-archiving.html Postgres is used by a wide gamut of people of differing abilities, many of who appreciate the availability of tested solutions to protect their data as they are not morons and understand there are people who can make their life easier. > This was actually my job as a consultant: to de-mystify technology, > and make it understandable as an arrangement of well explainable > pieces of functionality with well-deducible consequences. Not seeing it. > But this is no longer respected today; now people are expected to > *NOT* understand the technology they handle, and instead believe > in marketing and that it all is very complicated and un-intellegible. > > > cheerio, > PMc > -- Adrian Klaver adrian.klaver@aklaver.com
On Tue, Jun 09, 2020 at 03:42:48PM -0400, Stephen Frost wrote: ! > And then 90% of the things offered here become superfluous, because ! > they are already handled site-wide. And then you will have to ! > consider integration of both pieces - and that will most likely be ! > more work and more error-prone than just writing a few adapters in ! > shell. ! ! pgbackrest's repo can be safely backed up using the simple file-based ! backup utilities that you're referring to here. I suspect some of the ! other solution's backups also could be, but you'd probably want to make ! sure. What repo?? I seem to have missed that at first glance. Are You indeed suggesting that one should have their data within the database, where it is worked with, and then use Your tool to copy it to some "repo" disk playground whatever area, and then use their regular backup system to COPY IT AGAIN into their backup/archiving system? Are You kiddin'? Are You indeed suggesting that people should buy the amount of disks that they use for their database AGAIN in order for Your software to copy the stuff around? Is this becoming a madhouse, or are You going to refund them that? Let me tell You something: the people I used to work for, sometimes had a problem. They had some amount of data that was created during the day, and they had the night to write that data away to backup. That would usually mean, four or eight of the big tapes, streaming in parallel, fibers saturated, all night thru. And the problem usually was that they would need a longer night. At least the math had to be done properly. Maybe You never encountered these, but there are surroundings where there is no spare room for nonsense. Maybe that'S why these people preferred to use oracle. cheerio, PMc
On Wed, Jun 10, 2020 at 1:53 AM Peter <pmc@citylink.dinoex.sub.org> wrote:
On Tue, Jun 09, 2020 at 12:34:38PM -0700, Adrian Klaver wrote:
! The backup solution is?
https://www.bareos.com/
! Fine rant below. Go forth and work your wonders.
I don't need to, anymore. I did that, for about 20 years - people
I used to work for as a consultant (major banks and insurance shops)
would usually run Informix or Oracle. Postgres is just my own private
fancy.
On Tue, Jun 09, 2020 at 03:42:48PM -0400, Stephen Frost wrote:
! * Peter (pmc@citylink.dinoex.sub.org) wrote:
! > This professional backup solution also offers support for postgres.
! > Sadly, it only covers postgres up to Rel.9, and that piece of software
! > wasn't touched in the last 6 or 7 years.
!
! Then it certainly doesn't work with the changes in v12, and probably has
! other issues, as you allude to.
Just having a look at their webpage, something seems to have been updated
recently, they now state that they have a new postgres adapter:
https://www.bareos.com/en/company_news/postgres-plugin-en1.html
Enjoy reading, and tell us what You think.
This one unfortunately rings out of somebody who doesn't know how to back up postgres, at least in the past 10-15 years.
They are using an API that has been deprecated for years - in what's announced as a brand new product. They are advocating local archiving, which basically guarantees dataloss in the event of a disaster.
That's from a 3 minute look, but that's definitely enough to suggest this is not something I'd consider using.
! > Actually, I am getting very tired of reading that something which can
! > easily be done within 20 lines of shell scripting, would need special
!
! This is just simply false- you can't do it properly in 20 lines of shell
! scripting.
Well, Your own docs show how to do it with a one-liner. So please
don't blame me for improving that to 20 lines.
Yes, those docs are unfortunately "known bad" and should definitely be improved on. it does very clearly state that the example is just an example. But it doesn't clearly state *why* it shouldn't be used.
In my understanding, backup is done via pgdump. The archive logs are
for emergencies (data corruption, desaster), only. And emergencies
would usually be handled by some professional people who know what
they have to do.
I'd say it's the exact opposite. backups are done via pg_basebackup or manual basebackups. Archive logs are for point in time recovery. pg_dump can be used as a secondary "backup to the backups" option, but it is most interesting for things that are not backups (such as inspecting data, or provisioning partial test systems).
Different for different scenarios of course, but that would be the base scenario. And pg_dump are definitely as far from good backups are you can get while still having something that can be called approximately backups. It might be enough for small databases, but even in those cases pg_basebackup (without archive logging) is easier...
And yes, I read that whole horrible discussion, and I could tear my
hair out, really, concerning the "deprecated API". I suppose You mean
the mentioning in the docs that the "exclusive low-level backup" is
somehow deprecated.
Yes. There is no "somehow", it's deprecated.
This is a very big bad. Because: normally you can run the base backup
as a strictly ordinary file-level backup in "full" mode, just as any
backup software can do it. You will simply execute the
pg_start_backup() and pg_stop_backup() commands in the before- and
after- hooks - and any backup software will offer these hooks.
But now, with the now recommended "non-exclusive low-level backup",
the task is different: now your before-hook needs to do two things
at the same time:
1. keep a socket open in order to hold the connection to postgres
(because postgres will terminate the backup when the socket is
closed), and
2. invoke exit(0) (because the actual backup will not start until
the before- hook has properly delivered a successful exit code.
And, that is not only difficult, it is impossible.
It is not impossible. It is harder if you limit your available tools yes, but it also *works*.
So yes, this is really a LOT of work. But the point is: this all is
not really necessary, because currently the stuff works fine in the
old way.
It does not, no. It works in the simple cases, but it has multiple failure scenarios that *cannot* be fixed without changing those fundamentals.
But you can always go for the actual old way -- just stop postgres in the pre-job and start it again in the post-job. That's by far the easiest. And that *does* work and is fully supported.
! > The only really interesting thing there is the pg_probackup. These
! > folks seem to have found a way to do row-level incremental backups.
!
! pg_probackup doesn't do row-level incremental backups, unless I've
! missed some pretty serious change in its development, but it does
! provide page-level,
Ah, well, anyway that seems to be something significantly smaller
than the usual 1 gig table file at once.
pg_probackup does page level incremental *if* you install a postgres extension that some people have questioned the wisdom of (disclaimer: I have not looked at this particular extension, so I cannot comment on said wisdom). I think it also has some ability to do page level incremental by scanning WAL. But the bottom line is it's always page level, it's never going to be row level, based on the fundamentals of how PostgreSQL works.
Greetings, * Peter (pmc@citylink.dinoex.sub.org) wrote: > On Tue, Jun 09, 2020 at 03:42:48PM -0400, Stephen Frost wrote: > ! > And then 90% of the things offered here become superfluous, because > ! > they are already handled site-wide. And then you will have to > ! > consider integration of both pieces - and that will most likely be > ! > more work and more error-prone than just writing a few adapters in > ! > shell. > ! > ! pgbackrest's repo can be safely backed up using the simple file-based > ! backup utilities that you're referring to here. I suspect some of the > ! other solution's backups also could be, but you'd probably want to make > ! sure. > > What repo?? I seem to have missed that at first glance. Yes, pgbackrest has a repo, like most other tools (though they call them different things... pg_basebackup has one though it's not really formal). > Are You indeed suggesting that one should have their data within > the database, where it is worked with, and then use Your tool > to copy it to some "repo" disk playground whatever area, and then > use their regular backup system to COPY IT AGAIN into their > backup/archiving system? Are You kiddin'? No, I'm not kidding and yes, that's what I'm suggesting. You need a consistent backup of your database that includes all the needed WAL to perform a restore. This is only one option though, there are others- you can also use pgbackrest to push your backups to s3 (or any s3-compatible data storage system, which includes some backup systems), and we'll be adding support for Azure very shortly, and have plans to add GCS too in the future, along with others probably. > Is this becoming a madhouse, or are You going to refund them that? I concur that this is becoming a madhouse, and is pushing past the limit for what I'm willing to deal with when trying to assist someone. > Let me tell You something: the people I used to work for, sometimes > had a problem. They had some amount of data that was created during > the day, and they had the night to write that data away to backup. > That would usually mean, four or eight of the big tapes, streaming in > parallel, fibers saturated, all night thru. And the problem usually was > that they would need a longer night. At least the math had to be done > properly. Indeed, parallel backup is important, which is why pgbackrest supports it, along with compression and encryption, all in-stream between the database server and the repo, along with calculating a SHA to be stored of every single file seen, allowing you to validate that the files haven't changed since the backup was done when restoring. > Maybe You never encountered these, but there are surroundings where > there is no spare room for nonsense. Maybe that'S why these people > preferred to use oracle. I've both dealt with keeping tape drives fully loaded to avoid breaking the tape by studdering it (and writing dedicated C code to deal with exactly that), and dealt with backing up and restoring Oracle, including with various "enterprise" backup technologies (with varying levels of success...). None of what is being brought up here is new, novel, or even particularly interesting. Thanks, Stephen
Вложения
On Wed, Jun 10, 2020 at 01:10:36PM +0200, Magnus Hagander wrote: ! > Just having a look at their webpage, something seems to have been updated ! > recently, they now state that they have a new postgres adapter: ! > ! > https://www.bareos.com/en/company_news/postgres-plugin-en1.html ! > Enjoy reading, and tell us what You think. ! > ! ! This one unfortunately rings out of somebody who doesn't know how to back ! up postgres, at least in the past 10-15 years. ! ! They are using an API that has been deprecated for years - in what's ! announced as a brand new product. They are advocating local archiving, ! which basically guarantees dataloss in the event of a disaster. Aye, thank You, that's exactly the impression I got. This is probably still the old thing I was talking about, just made into a new product. ! That's from a 3 minute look, but that's definitely enough to suggest this ! is not something I'd consider using. The matter is, that backup software (as a whole, not this postgres component) offers lots of things exactly as I like them. It is a great concept, a great implementation, but a bad coding quality and a bad maintenance policy. But then, one can get it for free; and I know of no other with such features. So I went thru the effort of fixing it up, so that it now well serves my needs - and use my own scripting for the add-ons. ! > Well, Your own docs show how to do it with a one-liner. So please ! > don't blame me for improving that to 20 lines. ! > ! ! Yes, those docs are unfortunately "known bad" and should definitely be ! improved on. it does very clearly state that the example is just an ! example. But it doesn't clearly state *why* it shouldn't be used. That's why I felt the ethical need to speak up and share my consideration. Now it's up to those in charge and not my issue anymore. ;) ! In my understanding, backup is done via pgdump. The archive logs are ! > for emergencies (data corruption, desaster), only. And emergencies ! > would usually be handled by some professional people who know what ! > they have to do. ! > ! ! I'd say it's the exact opposite. backups are done via pg_basebackup or ! manual basebackups. Archive logs are for point in time recovery. pg_dump ! can be used as a secondary "backup to the backups" option, but it is most ! interesting for things that are not backups (such as inspecting data, or ! provisioning partial test systems). ! ! Different for different scenarios of course, but that would be the base ! scenario. And pg_dump are definitely as far from good backups are you can ! get while still having something that can be called approximately backups. ! It might be enough for small databases, but even in those cases ! pg_basebackup (without archive logging) is easier... It's easier to create - but to apply? That depends on how many DBs are in the cluster and how diverse their use. Also at any major version switch these backups get worthless; one cannot use them for longterm. (I suppose this is also true for pg_basebackup.) I'm creating my longterm (and offsite) simply as clones from the regular full backup. So what I came up with for now, is: I run pg_dump over all the present databases, plus globals, chunk that up (in a similar way like chunked HTTP works), feed it onto a pipe and backup that pipe. No need for interim storage, so it can get as large as the backup software can take it. And that should work for longterm - and I don't currently see a better option. (This one does not work in 20 lines shellscript, because I didn't get a reliable chunker running in shell.) ! And yes, I read that whole horrible discussion, and I could tear my ! > hair out, really, concerning the "deprecated API". I suppose You mean ! > the mentioning in the docs that the "exclusive low-level backup" is ! > somehow deprecated. ! > ! ! Yes. There is no "somehow", it's deprecated. Then lets not call it "somehow", as, more precisely, from my understanding so far, that so called "new API" is ill-conceived and troublesome in more than one regard. I would, with my current knowledge, recommend to avoid, or better, abandon it. Or, in other words: it is similar to what Boeing tried to do, in forcing things upon people via software, for safety reasons - and now see where Boeing got with that. ! > But now, with the now recommended "non-exclusive low-level backup", ! > the task is different: now your before-hook needs to do two things ! > at the same time: ! > 1. keep a socket open in order to hold the connection to postgres ! > (because postgres will terminate the backup when the socket is ! > closed), and ! > 2. invoke exit(0) (because the actual backup will not start until ! > the before- hook has properly delivered a successful exit code. ! > And, that is not only difficult, it is impossible. ! ! It is not impossible. It is harder if you limit your available tools yes, ! but it also *works*. In this description which I choose, I would think it is actually impossible. Certainly there are other ways to achieve it. But I also suppose that this is true: with the "new API" it is necessary to resort to (some kind of) threaded programming in order to use it. And properly handling threaded programming is significantly more error-prone than straight procedural code. I don't see why this should then be enforced in a case like this. ! It does not, no. It works in the simple cases, but it has multiple failure ! scenarios that *cannot* be fixed without changing those fundamentals. Then please tell me at least something about these scenarios. Then maybe one could think about some alternative approach that might suit these needs and still be enjoyable. ! But you can always go for the actual old way -- just stop postgres in the ! pre-job and start it again in the post-job. That's by far the easiest. And ! that *does* work and is fully supported. What? You seem to like ill jokes. Even if I would actually consider that, it wouldn't work, because the backup software itself has some database connections open during the backup. Not to talk about all the other apps that would need to be restarted. No, this has to be done in proper engineering, and with some beauty. After reading that deprecation message in the doc, the first thing I recognized was that this does NOT work in my current way with the before- and after- hooks, and that it will require an ugly amount of hackery and probably become unreliable when trying to make it work in that way. Then I got the idea that I could run pg_basebackup directly, and feed it on a pipe in the same way as I do with the pg_dumps. That one should work, as a kind of last resort. It is not sportsmanlike - there is no fun in climbing the same mountain twice. So currently I'm thinking about another option, that would actualize a base backup in the form of a power loss (which would then be transparent to the use of an API). ! > ! pg_probackup doesn't do row-level incremental backups, unless I've ! > ! missed some pretty serious change in its development, but it does ! > ! provide page-level, ! > ! > Ah, well, anyway that seems to be something significantly smaller ! > than the usual 1 gig table file at once. ! > ! ! pg_probackup does page level incremental *if* you install a postgres ! extension that some people have questioned the wisdom of (disclaimer: I ! have not looked at this particular extension, so I cannot comment on said ! wisdom). I think it also has some ability to do page level incremental by ! scanning WAL. But the bottom line is it's always page level, it's never ! going to be row level, based on the fundamentals of how PostgreSQL works. And a page is what I think it is - usually 8kB? That would have an effect of comparable magnitude, and would be nice, *if* it works properly. So thanks, I got the message and will search for the old discussion messages before looking closer into it. cheerio, PMc
On Wed, Jun 10, 2020 at 08:32:22AM -0400, Stephen Frost wrote:
! > What repo?? I seem to have missed that at first glance.
!
! Yes, pgbackrest has a repo, like most other tools (though they call them
! different things... pg_basebackup has one though it's not really
! formal).
!
! > Are You indeed suggesting that one should have their data within
! > the database, where it is worked with, and then use Your tool
! > to copy it to some "repo" disk playground whatever area, and then
! > use their regular backup system to COPY IT AGAIN into their
! > backup/archiving system? Are You kiddin'?
!
! No, I'm not kidding and yes, that's what I'm suggesting.
Well, do You think I could seriously sell that to anybody?
! You need a
! consistent backup of your database that includes all the needed WAL to
! perform a restore.
Okay. So lets behave like professional people and figure how that
can be achieved:
At first, we drop that WAL requirement, because with WAL archiving
it is already guaranteed that an unbroken chain of WAL is always
present in the backup (except when we have a bug like the one that
lead to this discussion).
So this is **not part of the scope**.
I'll get to the other item, the "consistent backup", further below.
! This is only one option though, there are others- you can also use
! pgbackrest to push your backups to s3 (or any s3-compatible data storage
! system, which includes some backup systems), and we'll be adding
! support
! I concur that this is becoming a madhouse, and is pushing past the limit
! for what I'm willing to deal with when trying to assist someone.
Well, then that might be a misconception. I'm traditionally a
consultant, and so I am used to *evaluate* solutions. I don't need
assistance for that, I only need precise technical info.
So lets get serious:
It is NOT technically feasible to amplify the storage in a way that
the entire backup data gets copied from the live database to some "repo"
place first, and then again from that repo place to regular file-based
backup/archiving storage.
And it does not make a difference WHERE that other place is, if at
Jeff's or whereever. It just does not belong into the loop.
So, how could the alternative look like?
I for my part consider doing this:
With a proper transactional filesystem we can do recursive filesystem
snapshots. That means, given a suitable filesystem layout, we can do a
snapshot of the data tree, AND the pg_wal filesystem, AND the
respective tablespaces. And this is atomical.
So, what we then do in the before- hook, is:
* we call pg_start_backup(whatever, false, false).
* we issue the filesystem snapshot, atomical.
* we call pg_stop_backup(whatever).
And then we return with exit(0) (if all succeeded), and the file-based
backup software can start to collect the files from the filesystem
snapshot, and release it afterwards.
This STILL needs threaded programming (as I said, there is no way to
avoid that with those "new API"), but in this case it is effectively
reduced to just grab the return-code of some program that has been
started with "&".
So far, so good.
There is still one thing to be done, namely, the requirement to
collect the data reported by pg_stop_backup() and add that to the
backup, at a point in time where that is ALREADY CLOSED! (that's
another piece of gross bogus in this "new API") - but with my intended
method (and some ugliness) this could now also be solved.
But then, lets think another step forward: for what purpose do we
actually need to call pg_start_backup() and pg_stop_backup() at all?
I couldn't find exhaustive information about that, only some partial
facts.
What we know for certain, is: if we leave these calls away, and
just do a filesystem snapshot and make a backup from that, then we
have exactly the same thing as if we had a power failure at that time.
So this is restoreable, and the server will certainly start.
The remaining question is: can we then give it our subsequently
archived redologs and make it roll forward before going ready? I don't
know that yet, but maybe, if we just throw these WAL into pg_wal, the
thing might be stupid enough to swallow them.
If that does not work, then there might still be ways to trick it
into believing it's a standby server and make it roll forward these
WAL.
So, there are not only ways to avoid the useless storage
amplification, there might even be means to get rid of that whole
misconceived "API".
Things that remain to be figured out:
1. What does pg_start_backup actually do and why would that be
necessary? I could not find exhaustive information, but this can
probably figured from the source. Currently I know so much:
- it writes a backup_label file. That is just a few lines of
ASCII and should not be difficult to produce.
- it does a checkpoint. This can probably be done with the
respective command (if it is needed at all).
- it does temporarily switch to full_page_writes. This cannot
be done interactively. So, item
2. why might it be necessary to have full_page_writes on? I'm
currently investigating into that one, but I might tend to assume
that this is just another piece of enforced Boeing-security, and
not really needed with a transactional filesystem.
I now hope very much that Magnus Hagander will tell some of the
impeding "failure scenarios", because I am getting increasingly
tired of pondering about probable ones, and searching the old
list entries for them, without finding something substantial.
cheerio,
PMc
Greetings, * Peter (pmc@citylink.dinoex.sub.org) wrote: > On Wed, Jun 10, 2020 at 08:32:22AM -0400, Stephen Frost wrote: > ! > What repo?? I seem to have missed that at first glance. > ! > ! Yes, pgbackrest has a repo, like most other tools (though they call them > ! different things... pg_basebackup has one though it's not really > ! formal). > ! > ! > Are You indeed suggesting that one should have their data within > ! > the database, where it is worked with, and then use Your tool > ! > to copy it to some "repo" disk playground whatever area, and then > ! > use their regular backup system to COPY IT AGAIN into their > ! > backup/archiving system? Are You kiddin'? > ! > ! No, I'm not kidding and yes, that's what I'm suggesting. > > Well, do You think I could seriously sell that to anybody? That hardly seems to have much relevance. I do know that there are lots of deployments which have exactly that setup though. > ! You need a > ! consistent backup of your database that includes all the needed WAL to > ! perform a restore. > > Okay. So lets behave like professional people and figure how that > can be achieved: No, thanks, but I'm done. I will not continue to engage with someone who insists on belittling everyone they engage with. That's not appropriate for any professional environment, including these lists. Thanks, Stephen
Вложения
On Thu, Jun 11, 2020 at 10:13 PM Peter <pmc@citylink.dinoex.sub.org> wrote:
Okay. So lets behave like professional people and figure how that
can be achieved:
At first, we drop that WAL requirement, because with WAL archiving
it is already guaranteed that an unbroken chain of WAL is always
present in the backup (except when we have a bug like the one that
lead to this discussion).
So this is **not part of the scope**.
I would assume that anybody who deals with backups professionally wouldn't consider that out of scope, but sure, for the sake of argument, let's do that.
! This is only one option though, there are others- you can also use
! pgbackrest to push your backups to s3 (or any s3-compatible data storage
! system, which includes some backup systems), and we'll be adding
! support
! I concur that this is becoming a madhouse, and is pushing past the limit
! for what I'm willing to deal with when trying to assist someone.
Well, then that might be a misconception. I'm traditionally a
consultant, and so I am used to *evaluate* solutions. I don't need
assistance for that, I only need precise technical info.
Excellent. Then let's stick to that.
This STILL needs threaded programming (as I said, there is no way to
avoid that with those "new API"), but in this case it is effectively
reduced to just grab the return-code of some program that has been
started with "&".
There is *absolutely* no need for threading to use the current APIs. You need to run one query, go do something else, and then run another query. It's 100% sequential, so there is zero need for threads. Now, if you're stuck in shellscript, it's a little more complicated. But it does not need threading.
But then, lets think another step forward: for what purpose do we
actually need to call pg_start_backup() and pg_stop_backup() at all?
I couldn't find exhaustive information about that, only some partial
facts.
Since you don't trust the documentation, I suggest you take a look at https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/access/transam/xlog.c;h=55cac186dc71fcc2f4628f9974b30850bb51eb5d;hb=92c58fd94801dd5c81ee20e26c5bb71ad64552a8#l10438
It has a fair amount of detail of the underlying reasons, and of course links to all the details.
Things that remain to be figured out:
1. What does pg_start_backup actually do and why would that be
necessary? I could not find exhaustive information, but this can
probably figured from the source. Currently I know so much:
- it writes a backup_label file. That is just a few lines of
ASCII and should not be difficult to produce.
It does that only in exclusive mode, and doing that is one of the big problems with exclusive mode. So don't do that.
I now hope very much that Magnus Hagander will tell some of the
impeding "failure scenarios", because I am getting increasingly
tired of pondering about probable ones, and searching the old
list entries for them, without finding something substantial.
Feel free to look at the mailinglist archives. Many of them have been explained there before. Pay particular attention to the threads around when the deprecated APIs were actually deprecaed. I believe somebody around that time also wrote a set of bash scripts that can be used in a pre/post-backup-job combination with the current APIs.
//Magnus
On Thu, 2020-06-11 at 22:35 +0200, Magnus Hagander wrote: > I believe somebody around that time also wrote a set of bash scripts that can be used in a pre/post-backup-job combinationwith the current APIs. https://github.com/cybertec-postgresql/safe-backup Yours, Laurenz Albe -- Cybertec | https://www.cybertec-postgresql.com
Greetings, * Adrian Klaver (adrian.klaver@aklaver.com) wrote: > On 6/9/20 4:15 AM, Stephen Frost wrote: > >* Adrian Klaver (adrian.klaver@aklaver.com) wrote: > >>I use pg_backrest, but it does not look promising for running on BSD: > >>https://fluca1978.github.io/2019/03/04/pgbackrest_FreeBSD.html > > > >That's an unfortunately ancient post, really, considering that > >pgbackrest has now been fully rewritten into C, and Luca as recently as > >September 2019 was saying he has it working on FreeBSD. > > Yeah, but this: > > https://github.com/pgbackrest/pgbackrest/issues/686 > > is not clear on whether a user can do that w/o a certain amount of hand > holding. Luca (at my asking) wrote up a new blog post to clarify things, you can see it here: https://fluca1978.github.io/2020/06/12/pgbackrestOnFreeBSD.html No particular hand holding needed. Thanks, Stephen
Вложения
On Thu, Jun 11, 2020 at 10:53:15PM +0200, Laurenz Albe wrote: ! On Thu, 2020-06-11 at 22:35 +0200, Magnus Hagander wrote: ! > I believe somebody around that time also wrote a set of bash scripts that can be used in a pre/post-backup-job combinationwith the current APIs. ! ! https://github.com/cybertec-postgresql/safe-backup Ah, thank You, very nice. I've never seen anybody coding bash - it is strongly shunned in the Berkeley community. Some Questions: 1. There are explicit error messages in loc-82 and -92 of pgpre.sh. To where are these written? 2. The result data from pg_stop_backup() are stored into the living database. But, according to the docs, they should be placed into the completed backup. Do I have a misunderstanding here? 3. The most common error cause of a backup might be tape-side malfunction. So far as I see, the way to handle this is currently, to provide a timeout for pgpre.sh (which is problematic, because we might as well have just reached end-of-tape and have to wait until monday for the operator to change it). May I suggest to add a switch to pgpost.sh, in order to volutarily fail out of the job? 4. If, by misconfiguration and/or operator error, the backup system happens to start a second backup. in parallel to the first, then do I correctly assume, both backups will be rendered inconsistent while this may not be visible to the operator; and the earlier backup would be flagged as apparently successful while carrying the wrong (later) label? BTW: what does, in general, happen, if a backup_label file gets accidentially swapped with one from a parallel, but slightly later backup? Do I correctly assume that such mistake gets somehow detected, as otherwise it would have just the same unwelcome effects (i.e. silent data corruption) as no backup_label at all? cheerio, PMc
On Sat, 2020-06-13 at 05:24 +0200, Peter wrote: > ! https://github.com/cybertec-postgresql/safe-backup > > Ah, thank You, very nice. > > I've never seen anybody coding bash - it is strongly shunned in the > Berkeley community. Strange, but then I don't move in these circles. > Some Questions: > 1. There are explicit error messages in loc-82 and -92 of pgpre.sh. > To where are these written? Standard error. It is up to the caller of the script to route that somewhere useful. > 2. The result data from pg_stop_backup() are stored into the living > database. But, according to the docs, they should be placed into > the completed backup. Do I have a misunderstanding here? Right, but these scripts don't know anything about that backup itself. They are designed to be called before and after the backup. In between, you back up the data directory however you think fit. It is the responsibility of the caller of the post-backup script to add the "backup_label" file to the backup. > 3. The most common error cause of a backup might be tape-side > malfunction. So far as I see, the way to handle this is currently, > to provide a timeout for pgpre.sh (which is problematic, because > we might as well have just reached end-of-tape and have to wait > until monday for the operator to change it). May I suggest to add > a switch to pgpost.sh, in order to volutarily fail out of the job? As said above, the backup itself is not the job of these scripts. > 4. If, by misconfiguration and/or operator error, the backup system > happens to start a second backup. in parallel to the first, > then do I correctly assume, both backups will be rendered > inconsistent while this may not be visible to the operator; and > the earlier backup would be flagged as apparently successful while > carrying the wrong (later) label? If you are using my scripts and start a second backup while the first one is still running, the first backup will be interrupted. This is specific to my scripts, PostgreSQL's non-exclusive backup can perform more than one concurrent backup successfully. I tried to keep things simple. > BTW: what does, in general, happen, if a backup_label file gets > accidentially swapped with one from a parallel, but slightly later > backup? Do I correctly assume that such mistake gets somehow detected, > as otherwise it would have just the same unwelcome effects > (i.e. silent data corruption) as no backup_label at all? If you have the wrong "backup_label", you end up with silent data corruption. That should not happen with my scripts, though. Yours, Laurenz Albe -- Cybertec | https://www.cybertec-postgresql.com
On Sat, Jun 13, 2020 at 01:53:28PM +0200, Laurenz Albe wrote: ! > I've never seen anybody coding bash - it is strongly shunned in the ! > Berkeley community. ! ! Strange, but then I don't move in these circles. Never mind. ! > Some Questions: ! > 1. There are explicit error messages in loc-82 and -92 of pgpre.sh. ! > To where are these written? ! ! Standard error. It is up to the caller of the script to route that ! somewhere useful. Understood. ! > 2. The result data from pg_stop_backup() are stored into the living ! > database. But, according to the docs, they should be placed into ! > the completed backup. Do I have a misunderstanding here? ! ! Right, but these scripts don't know anything about that backup itself. ! They are designed to be called before and after the backup. ! In between, you back up the data directory however you think fit. ! ! It is the responsibility of the caller of the post-backup script ! to add the "backup_label" file to the backup. I see. ! > 4. If, by misconfiguration and/or operator error, the backup system ! > happens to start a second backup. in parallel to the first, ! > then do I correctly assume, both backups will be rendered ! > inconsistent while this may not be visible to the operator; and ! > the earlier backup would be flagged as apparently successful while ! > carrying the wrong (later) label? ! ! If you are using my scripts and start a second backup while the first ! one is still running, the first backup will be interrupted. This is not what I am asking. It appears correct to me, that, on the database, the first backup will be interrupted. But on the tape side, this might go unnoticed, and on completion it will successfully receive the termination code from the *SECOND* backup - which means that on tape we will have a seemingly successful backup, which 1. is corrupted, and 2. carries a wrong label. ! This is specific to my scripts, PostgreSQL's non-exclusive backup ! can perform more than one concurrent backup successfully. ! I tried to keep things simple. I understand. But the operator may not know that and/or accidentially start a second backup while one is still running. And this will then result in ... ! If you have the wrong "backup_label", you end up with silent data corruption. ... this. Indeed this is difficult to avoid, because the high risk of silent data corruption is an elementary architectural feature of the so-called "new API". Which is why this is not going to run on my ship. But you will have to wait - the to-be-expected inrush of service-sales due to corrupted clusters will only happen after R.13 is active and peope are *forced* to cope with that "new API". Thanks for the effort of answering my questions. cheerio, PMc
On Thu, Jun 11, 2020 at 10:35:13PM +0200, Magnus Hagander wrote: ! > Okay. So lets behave like professional people and figure how that ! > can be achieved: ! > At first, we drop that WAL requirement, because with WAL archiving ! > it is already guaranteed that an unbroken chain of WAL is always ! > present in the backup (except when we have a bug like the one that ! > lead to this discussion). ! > So this is **not part of the scope**. ! > ! ! I would assume that anybody who deals with backups professionally wouldn't ! consider that out of scope, I strongly disagree. I might suppose You haven't thought this to the proper end. See: The WAL backup is, for a couple of reasons, different to most other backup objects: - it runs on demand, not per schedule. - it must be immediately repeated (or alerted), until success, otherwise the database might stop. - it might use a different storage (e.g. twofold/mirrored), for obvious reasons. - it gets deleted after backup, and that is a point-of-no-return. For the data tree backup, on the contrary, all these attributes are identical to those of any other incr/full filesystem backup. You can see that all the major attributes (scheduling, error-handling, signalling, ...) of a WAL backup are substantially different to that of any usual backup. This is a different *Class* of backup object, therefore it needs an appropriate infrastructure that can handle these attributes correctly. The WAL do *not belong* into the scope of the data tree backup, they are to be handled by different schemes in a different way. But, if You never have considered *continuous* archiving, and only intend to take a functional momentarily backup of a cluster, then You may well have never noticed these differences. I noticed them mainly because I did *BUILD* such an infrastructure (the 20 lines of shell script, you know). And yes, I was indeed talking about *professional* approaches. ! There is *absolutely* no need for threading to use the current APIs. You ! need to run one query, go do something else, and then run another ! query. Wrong. The point is, I dont want to "go do something else", I have to exit() and get back to the initiator at that place. This is also clearly visible in Laurenz' code: he utilizes two unchecked background tasks (processes, in this case) with loose coupling for the purpose, as it does not work otherwise. ! But then, lets think another step forward: for what purpose do we ! > actually need to call pg_start_backup() and pg_stop_backup() at all? ! > I couldn't find exhaustive information about that, only some partial ! > facts. ! > ! ! Since you don't trust the documentation, I suggest you take a look at ! https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/access/transam/xlog.c;h=55cac186dc71fcc2f4628f9974b30850bb51eb5d;hb=92c58fd94801dd5c81ee20e26c5bb71ad64552a8#l10438 Thanks, this indeed gives a most entertaining read. Honestly, I've never seen such a source before - there is thrice as much storytime than code. :) The most interesting point in there appears to be this: > that the backup label and tablespace map files are not written to > disk. Instead, their would-be contents are returned in *labelfile > and *tblspcmapfile, This is in do_pg_start_backup() - so we actually HAVE this data already at the *START* time of the backup! Then why in hell do we wait until the END of the backup before we hand this data to the operator: at a time when the DVD with the backup is already fixated and cannot be changed anymore, so that we have to send this data to quarternary storage (spell: the line printer) and have girl Friday sort them out (and probably mix them up)?? Is this indeed Boeing-security: try to avoid possible mistake by creating a much bigger risk? ! Things that remain to be figured out: ! > 1. What does pg_start_backup actually do and why would that be ! > necessary? I could not find exhaustive information, but this can ! > probably figured from the source. Currently I know so much: ! > - it writes a backup_label file. That is just a few lines of ! > ASCII and should not be difficult to produce. ! > ! ! It does that only in exclusive mode, and doing that is one of the big ! problems with exclusive mode. So don't do that. As I can read, there is no difference in the function requirements between exclusive and non-exclusive mode, in that regard: the backup-label file is NOT necessary in the running cluster data tree, BUT it should get into the RESTORED data tree before starting it. And I can't find a single one of those "big problems". What I do find is just people whining that their cluster doesn't start and they can't simply delete a file, even if told so. Like soldier complaining that his gun doesn't shoot and he has no idea how to reload. I could devise a dozen ways how to detect that situation automatically during rc.d and remove the file - if it were of any concern to me. ! > I now hope very much that Magnus Hagander will tell some of the ! > impeding "failure scenarios", because I am getting increasingly ! > tired of pondering about probable ones, and searching the old ! > list entries for them, without finding something substantial. ! Feel free to look at the mailinglist archives. Many of them have been ! explained there before. Pay particular attention to the threads around when ! the deprecated APIs were actually deprecaed. I *DID* read all that stuff. About hundred messages. It is HORRIBLE. I was tearing out my hair in despair. To subsume: it all circles around catering for gross pilot error and stupidity. cheerio, PMc
On Sat, Jun 13, 2020 at 10:13 PM Peter <pmc@citylink.dinoex.sub.org> wrote:
On Thu, Jun 11, 2020 at 10:35:13PM +0200, Magnus Hagander wrote:
! > Okay. So lets behave like professional people and figure how that
! > can be achieved:
! > At first, we drop that WAL requirement, because with WAL archiving
! > it is already guaranteed that an unbroken chain of WAL is always
! > present in the backup (except when we have a bug like the one that
! > lead to this discussion).
! > So this is **not part of the scope**.
! >
!
! I would assume that anybody who deals with backups professionally wouldn't
! consider that out of scope,
I strongly disagree. I might suppose You haven't thought this to the
proper end. See:
You may disagree, but I would argue that this is because you are the one who has not thought it through. But hey, let's agree to disagree.
You can see that all the major attributes (scheduling, error-handling,
signalling, ...) of a WAL backup are substantially different to that
of any usual backup.
This is a different *Class* of backup object, therefore it needs an
appropriate infrastructure that can handle these attributes correctly.
Yes, this is *exactly* why special-handling the WAL during the base backup makes a lot of sense.
Is it required? No.
Will it make your backups more reliable? Yes.
But it depends on what your priorities are.
But, if You never have considered *continuous* archiving, and only
intend to take a functional momentarily backup of a cluster, then You
may well have never noticed these differences. I noticed them mainly
because I did *BUILD* such an infrastructure (the 20 lines of shell
script, you know).
Yes, if you take a simplistic view of your backups, then yes.
And yes, I was indeed talking about *professional* approaches.
Sure.
! There is *absolutely* no need for threading to use the current APIs. You
! need to run one query, go do something else, and then run another
! query.
Wrong. The point is, I dont want to "go do something else", I have to
exit() and get back to the initiator at that place.
That is not a requirement of the current PostgreSQL APIs. (in fact, using threading would add a significant extra burden there, as libpq does not allow sharing of connections between threads)
That is a requirement, and indeed a pretty sharp limitation, of the *other* APIs you are working with, it sounds like.
The PostgreSQL APIs discussed to *not* require you to do an exit(). Nor do they require any form of threading.
And the fact that you need to do an exit() would negate any threading anyway, so that seems to be a false argument regardless.
This is also clearly visible in Laurenz' code: he utilizes two
unchecked background tasks (processes, in this case) with loose
coupling for the purpose, as it does not work otherwise.
Yes, because he is also trying to work around a severely limited API *on the other side*.
There's plenty of backup integrations that don't have this limitation. They all work perfectly fine with no need for exit() and certainly no weird need for special threading.
The most interesting point in there appears to be this:
> that the backup label and tablespace map files are not written to
> disk. Instead, their would-be contents are returned in *labelfile
> and *tblspcmapfile,
This is in do_pg_start_backup() - so we actually HAVE this data
already at the *START* time of the backup!
Then why in hell do we wait until the END of the backup before we
hand this data to the operator: at a time when the DVD with the
Because it cannot be safely written *into the data directory*.
Now, it could be written *somewhere else*, that is true. And then you would add an extra step at restore time to rename it back. But then your restore would now also require a plugin.
(
backup is already fixated and cannot be changed anymore, so that
You don't need to change the the backup, only append to it. If you are calling pg_stop_backup() at a time when that is no longer possible, then you are calling pg_stop_backup() at the wrong time.
As I can read, there is no difference in the function requirements
between exclusive and non-exclusive mode, in that regard: the
backup-label file is NOT necessary in the running cluster data tree,
BUT it should get into the RESTORED data tree before starting it.
Correct. It is in fact actively harmful in the running cluster data tree.
And I can't find a single one of those "big problems". What I do find
is just people whining that their cluster doesn't start and they can't
simply delete a file, even if told so. Like soldier complaining that
his gun doesn't shoot and he has no idea how to reload.
Have you actually tried it? Or dealt with the many people who have run into corruption around this?
Again, as suggested before, review the discussions that led up to the changes. There are plenty of examples there.
! > I now hope very much that Magnus Hagander will tell some of the
! > impeding "failure scenarios", because I am getting increasingly
! > tired of pondering about probable ones, and searching the old
! > list entries for them, without finding something substantial.
! Feel free to look at the mailinglist archives. Many of them have been
! explained there before. Pay particular attention to the threads around when
! the deprecated APIs were actually deprecaed.
I *DID* read all that stuff. About hundred messages. It is HORRIBLE.
I was tearing out my hair in despair.
To subsume: it all circles around catering for gross pilot error and
stupidity.
Yes, and people not reading the documentation. Or not liking what they read and therefore ignoring it.
//Magnus
On Sat, 2020-06-13 at 19:48 +0200, Peter wrote: > ! > 4. If, by misconfiguration and/or operator error, the backup system > ! > happens to start a second backup. in parallel to the first, > ! > then do I correctly assume, both backups will be rendered > ! > inconsistent while this may not be visible to the operator; and > ! > the earlier backup would be flagged as apparently successful while > ! > carrying the wrong (later) label? > ! > ! If you are using my scripts and start a second backup while the first > ! one is still running, the first backup will be interrupted. > > This is not what I am asking. It appears correct to me, that, on > the database, the first backup will be interrupted. But on the > tape side, this might go unnoticed, and on completion it will > successfully receive the termination code from the *SECOND* > backup - which means that on tape we will have a seemingly > successful backup, which > 1. is corrupted, and > 2. carries a wrong label. That will only happen if the backup that uses my scripts does the wrong thing. An example: - Backup #1 calls "pgpre.sh" - Backup #1 starts copying files - Backup #2 calls "pgpre.sh". This will cancel the first backup. - Backup #1 completes copying files. - Backup #1 calls "pgpost.sh". It will receive an error. So it has to invalidate the backup. - Backup #2 completes copying files. - Backup #2 calls "pgpost.sh". It gets a "backup_label" file and completes the backup. So the only way that something can go wrong would be if backup #1 somehow does *not* invalidate the backup. > ! This is specific to my scripts, PostgreSQL's non-exclusive backup > ! can perform more than one concurrent backup successfully. > ! I tried to keep things simple. > > I understand. But the operator may not know that and/or accidentially > start a second backup while one is still running. And this will then > result in ... > > ! If you have the wrong "backup_label", you end up with silent data corruption. > > ... this. Of course, if you do arbitrary nonsense like restoring a backup without "backup_label", you will get arbitrary data corruption. It is a fundamental principle that, apart from "backup_label", there is no way to tell a backup from a crashed data directory. Any backup/recovery software must refuse to use a backup that lacks that file. Yours, Laurenz Albe -- Cybertec | https://www.cybertec-postgresql.com
On Mon, Jun 15, 2020 at 11:44:33AM +0200, Laurenz Albe wrote:
! On Sat, 2020-06-13 at 19:48 +0200, Peter wrote:
! > ! > 4. If, by misconfiguration and/or operator error, the backup system
! > ! > happens to start a second backup. in parallel to the first,
! > ! > then do I correctly assume, both backups will be rendered
! > ! > inconsistent while this may not be visible to the operator; and
! > ! > the earlier backup would be flagged as apparently successful while
! > ! > carrying the wrong (later) label?
! > !
! > ! If you are using my scripts and start a second backup while the first
! > ! one is still running, the first backup will be interrupted.
! >
! > This is not what I am asking. It appears correct to me, that, on
! > the database, the first backup will be interrupted. But on the
! > tape side, this might go unnoticed, and on completion it will
! > successfully receive the termination code from the *SECOND*
! > backup - which means that on tape we will have a seemingly
! > successful backup, which
! > 1. is corrupted, and
! > 2. carries a wrong label.
!
! That will only happen if the backup that uses my scripts does the
! wrong thing.
Yes. Occasionally software does the wrong thing, it's called "bugs".
! An example:
!
! - Backup #1 calls "pgpre.sh"
! - Backup #1 starts copying files
! - Backup #2 calls "pgpre.sh".
! This will cancel the first backup.
! - Backup #1 completes copying files.
! - Backup #1 calls "pgpost.sh".
! It will receive an error.
! So it has to invalidate the backup.
! - Backup #2 completes copying files.
! - Backup #2 calls "pgpost.sh".
! It gets a "backup_label" file and completes the backup.
That's not true.
Now let me see how to compile a bash... and here we go:
! An example:
!
! - Backup #1 calls "pgpre.sh"
> $ ./pgpre.sh
> backup starting location: 1/C8000058
> $
We now have:
> 24129 10 SJ 0:00.00 /usr/local/bin/bash ./pgpre.sh
> 24130 10 SJ 0:00.00 /usr/local/bin/bash ./pgpre.sh
> 24131 10 SJ 0:00.01 psql -Atq
> 24158 10 SCJ 0:00.00 sleep 5
And:
> postgres=# \d
> List of relations
> Schema | Name | Type | Owner
> --------+--------+-------+----------
> public | backup | table | postgres
> (1 row)
>
> postgres=# select * from backup;
> id | state | pid | backup_label | tablespace_map
> ----+---------+-------+--------------+----------------
> 1 | running | 24132 | |
> (1 row)
! - Backup #1 starts copying files
Let's suppose it does now.
! - Backup #2 calls "pgpre.sh".
> $ ./pgpre.sh
> backup starting location: 1/C9000024
> $ FATAL: terminating connection due to administrator command
> server closed the connection unexpectedly
> This probably means the server terminated abnormally
> before or while processing the request.
> connection to server was lost
> Backup failed
> ./pgpre.sh: line 93: ${PSQL[1]}: ambiguous redirect
>
> $ echo $?
> 0
! This will cancel the first backup.
Yes, it seems it did:
> 25279 10 SJ 0:00.00 /usr/local/bin/bash ./pgpre.sh
> 25280 10 IWJ 0:00.00 /usr/local/bin/bash ./pgpre.sh
> 25281 10 SJ 0:00.01 psql -Atq
> 25402 10 SCJ 0:00.00 sleep 5
> postgres=# \d
> List of relations
> Schema | Name | Type | Owner
> --------+--------+-------+----------
> public | backup | table | postgres
> (1 row)
>
> postgres=# select * from backup;
> id | state | pid | backup_label | tablespace_map
> ----+---------+-------+--------------+----------------
> 1 | running | 25282 | |
> (1 row)
! - Backup #1 completes copying files.
! - Backup #1 calls "pgpost.sh".
> $ ./pgpost.sh
> START WAL LOCATION: 1/C9000024 (file 0000000100000001000000C9)
> CHECKPOINT LOCATION: 1/C9000058
> BACKUP METHOD: streamed
> BACKUP FROM: master
> START TIME: 2020-06-15 14:09:41 CEST
> LABEL: 2020-06-15 14:09:40
> START TIMELINE: 1
>
> $ echo $?
> 0
! It will receive an error.
! So it has to invalidate the backup.
Where is the error?
What we now have is this:
No processes anymore.
> id | state | pid | backup_label | tablespace_map
> ----+----------+-------+----------------------------------------------------------------+----------------
> 1 | complete | 25282 | START WAL LOCATION: 1/C9000024 (file 0000000100000001000000C9)+|
> | | | CHECKPOINT LOCATION: 1/C9000058 +|
> | | | BACKUP METHOD: streamed +|
> | | | BACKUP FROM: master +|
> | | | START TIME: 2020-06-15 14:09:41 CEST +|
> | | | LABEL: 2020-06-15 14:09:40 +|
> | | | START TIMELINE: 1 +|
> | | | |
> (1 row)
! - Backup #2 completes copying files.
! - Backup #2 calls "pgpost.sh".
! It gets a "backup_label" file and completes the backup.
Wishful thinking.
BOTH backups are now inconsistent, and the first got the label from
the second, and appears to be intact. Exactly as I said before.
I don't need to try such things out. I can do logical verification in
my mind, by looking at the code.
And on the same foundation I am saying that this whole new API is a
misconception.
cheerio,
PMc
On Mon, 2020-06-15 at 14:50 +0200, Peter wrote: > ! An example: > ! > ! - Backup #1 calls "pgpre.sh" > ! - Backup #1 starts copying files > ! - Backup #2 calls "pgpre.sh". > ! This will cancel the first backup. > ! - Backup #1 completes copying files. > ! - Backup #1 calls "pgpost.sh". > ! It will receive an error. > ! So it has to invalidate the backup. > ! - Backup #2 completes copying files. > ! - Backup #2 calls "pgpost.sh". > ! It gets a "backup_label" file and completes the backup. > > That's not true. Ah, yes, you are right. It's a while since I wrote these scripts. Since "pgpre.sh" and "pgpost.sh" are independent, there is no way to tell which of them belongs to which other. So calling "pgpost.sh" indeed ends the most recently started backup and returns "backup_label" accordingly. That means: the caller of the scripts has to make sure not to start a second backup while the first one is running. Yours, Laurenz Albe -- Cybertec | https://www.cybertec-postgresql.com
On Mon, Jun 15, 2020 at 03:19:29PM +0200, Laurenz Albe wrote: ! On Mon, 2020-06-15 at 14:50 +0200, Peter wrote: ! > ! An example: ! > ! ! > ! - Backup #1 calls "pgpre.sh" ! > ! - Backup #1 starts copying files ! > ! - Backup #2 calls "pgpre.sh". ! > ! This will cancel the first backup. ! > ! - Backup #1 completes copying files. ! > ! - Backup #1 calls "pgpost.sh". ! > ! It will receive an error. ! > ! So it has to invalidate the backup. ! > ! - Backup #2 completes copying files. ! > ! - Backup #2 calls "pgpost.sh". ! > ! It gets a "backup_label" file and completes the backup. ! > ! > That's not true. ! ! Ah, yes, you are right. Thank You. ! Since "pgpre.sh" and "pgpost.sh" are independent, there ! is no way to tell which of them belongs to which other. Correct. ! So calling "pgpost.sh" indeed ends the most recently started ! backup and returns "backup_label" accordingly. ! ! That means: the caller of the scripts has to make sure ! not to start a second backup while the first one is running. Never run two backups in parallel with such an approach, exactly. And that is one of a couple of likely pitfalls I perceived when looking at that new API. We could fix that, but that will then get more complicated - and people will usually not do that. And that's why I consider that new API as rather dangerous. cheerio, PMc
On Mon, 2020-06-15 at 19:00 +0200, Peter wrote: > And that is one of a couple of likely pitfalls I perceived when > looking at that new API. That is a property of my scripts, *not* of the non-exclusive backup API... > We could fix that, but that will then get more complicated - and > people will usually not do that. And that's why I consider that > new API as rather dangerous. ... so this is moot. Yours, Laurenz Albe
On Sun, Jun 14, 2020 at 03:05:15PM +0200, Magnus Hagander wrote: ! > You can see that all the major attributes (scheduling, error-handling, ! > signalling, ...) of a WAL backup are substantially different to that ! > of any usual backup. ! ! > This is a different *Class* of backup object, therefore it needs an ! > appropriate infrastructure that can handle these attributes correctly. ! > ! ! Yes, this is *exactly* why special-handling the WAL during the base backup ! makes a lot of sense. Certainly. Only I prefer to do the special-handling *outside of* the base backup. ! Is it required? No. ! Will it make your backups more reliable? Yes. *shrug* I have no benefit in increasing reliability from 250% to 330%, if that would be the case at all. ! But, if You never have considered *continuous* archiving, and only ! > intend to take a functional momentarily backup of a cluster, then You ! > may well have never noticed these differences. I noticed them mainly ! > because I did *BUILD* such an infrastructure (the 20 lines of shell ! > script, you know). ! > ! ! Yes, if you take a simplistic view of your backups, then yes. You appear to sound like an insurance salesman who desperately tries to sell a third health insurance policy to somebody who already has two of them, by trying to build on unfounded precariousness. ! ! There is *absolutely* no need for threading to use the current APIs. You ! > ! need to run one query, go do something else, and then run another ! > ! query. ! > ! > Wrong. The point is, I dont want to "go do something else", I have to ! > exit() and get back to the initiator at that place. ! > ! ! That is not a requirement of the current PostgreSQL APIs. We'll be done with that whole API in a few more lines now. (I'm getting tired of this.) ! (in fact, using ! threading would add a significant extra burden there, as libpq does not ! allow sharing of connections between threads) I never said one would need to thread the DB connections. ! That is a requirement, and indeed a pretty sharp limitation, of the *other* ! APIs you are working with, it sounds like. What "other"? ! The PostgreSQL APIs discussed to *not* require you to do an exit(). Nor do ! they require any form of threading. Ah, nice try! But, we're *NOT* shifting blame around. We do instead get things working. We do proper engineering. ! And the fact that you need to do an exit() would negate any threading ! anyway, so that seems to be a false argument regardless. You do know exactly what I'm talking about. ! This is also clearly visible in Laurenz' code: he utilizes two ! > unchecked background tasks (processes, in this case) with loose ! > coupling for the purpose, as it does not work otherwise. ! > ! ! Yes, because he is also trying to work around a severely limited API *on ! the other side*. There is no "other" side. There is only *one* side: to get things working. And for interaction, Jon Postel's law applies: Be conservative in what you provide, and liberal in what you require. This is how the Internet was built. The modern-day linux-youngsters tend to forget that we all stand on the shoulders of giants. ! The most interesting point in there appears to be this: ! > > that the backup label and tablespace map files are not written to ! > > disk. Instead, their would-be contents are returned in *labelfile ! > > and *tblspcmapfile, ! > ! > This is in do_pg_start_backup() - so we actually HAVE this data ! > already at the *START* time of the backup! ! ! ! > Then why in hell do we wait until the END of the backup before we ! > hand this data to the operator: at a time when the DVD with the ! > ! ! Because it cannot be safely written *into the data directory*. ! ! Now, it could be written *somewhere else*, that is true. And then you would ! add an extra step at restore time to rename it back. But then your restore ! would now also require a plugin. Yes, and as it is now, it requires girl Friday to fetch them from the line-printer and mix them up - which, as we already got explained, can end up a *lot* worse. Or, equivalently and as here practically demonstrated, some consultant trainee writing some script which, when accidentially invoked twice, creates an inconsistent backup, and this being invisible to the operator. That's indeed dangerous enough for my taste. But lets grab that from the start: Yes, I didn't trust the docs. Because, as people here are so crazy about the old API being troublesome and dangerous and must be deprecated, and the whole thing being so imminent, then there should be some REASON for that. And from the docs I could not see any reason - so I supposed there must be something else in pg_start_backup(); something that is not explained in the docs, and that would explain the whole bohei. But, in fact, there is no such thing. First, the backup_label, which should not stay in the running cluster tree. So, what bad does happen when it stays there? Nothing at all. The cluster might not start at once. But then, there was a CRASH before - and there it is normal for some things to be messed. And, anyway, on productive machines a crash is not supposed to happen. But nevertheless, this can be solved, by simply deleting the backup_label during /etc/rc. What bad could then happen from doing that? Actually nothing - because the backup_label is only needed between restore and rollforward. And there is no reboot required between restore and rollforward. If a power-loss might happen during restore - start anew with a clean restore. If a power-loss might happen during rollforward - start anew with a clean restore. And then, fix the diesel. So much for the backup_label. Furthermore, if there is some means of filesystem snapshots, the backup_label is entirely superfluous. Next, the checkpoint. That's needed if one wants to build up a timeline-zoo, and to engage full_page_writes. I prefer to have neither of these. Finally, the full_page_writes. The only problem here can be if Postgres itself writes a block in piecemeal fashion. Otherwise there will always visible either the old content or the new content, never something in-between. Because there is only one pointer to the block, and that does contain a single value. (But indeed, that might not be true on a quantum computer, or with a non-transactional filesystem like they happen to have on linux.) So, issue debunked. ! > backup is already fixated and cannot be changed anymore, so that ! > ! ! You don't need to change the the backup, only append to it. If you are ! calling pg_stop_backup() at a time when that is no longer possible, then ! you are calling pg_stop_backup() at the wrong time. It's not trivial to add something to a stream after the fact. ! As I can read, there is no difference in the function requirements ! > between exclusive and non-exclusive mode, in that regard: the ! > backup-label file is NOT necessary in the running cluster data tree, ! > BUT it should get into the RESTORED data tree before starting it. ! ! Correct. It is in fact actively harmful in the running cluster data tree. Great, we're getting to the point - the remaining problem seems that we have done away with corporal punishment, so people no longer have a clear understanding about what "actively harmful" means. ! And I can't find a single one of those "big problems". What I do find ! > is just people whining that their cluster doesn't start and they can't ! > simply delete a file, even if told so. Like soldier complaining that ! > his gun doesn't shoot and he has no idea how to reload. ! > ! ! Have you actually tried it? Or dealt with the many people who have run into ! corruption around this? I wasn't able to reproduce the problem. But indeed I do know that skill-levels in general are vastly going down the gully and are already reaching chthonian levels; and the more so since GitHub et al. have decided to ban mastery. So, if folks run into corruption, that is no surprise, since it was *them* who have actively decided to fire all the experienced DBAs and have the stuff done from Malaysia instead, for cheap. Their business equates their business, and I couldn't care less. Caee dismissed. cheerio, PMc
On Mon, Jun 15, 2020 at 09:46:34PM +0200, Laurenz Albe wrote: ! On Mon, 2020-06-15 at 19:00 +0200, Peter wrote: ! > And that is one of a couple of likely pitfalls I perceived when ! > looking at that new API. ! ! That is a property of my scripts, *not* of the non-exclusive ! backup API... Then how would I have figured it before even knowing Your scripts? The API requires such kind of programming, and such kind of programming creates dangerous pitfalls. After You have trained soms hundreds of system administrators, You will also see such things right at first glance. But then it's futile to discuss with religious people, as they are blind to reasoning: AL II. 58, "The slaves shall serve." cheerio, PMc
On Tue, 2020-06-16 at 00:28 +0200, Peter wrote: > On Mon, Jun 15, 2020 at 09:46:34PM +0200, Laurenz Albe wrote: > ! On Mon, 2020-06-15 at 19:00 +0200, Peter wrote: > ! > And that is one of a couple of likely pitfalls I perceived when > ! > looking at that new API. > ! > ! That is a property of my scripts, *not* of the non-exclusive > ! backup API... > > Then how would I have figured it before even knowing Your scripts? By reading the documentation and trying it? > The API requires such kind of programming, and such kind of > programming creates dangerous pitfalls. After You have trained soms > hundreds of system administrators, You will also see such things > right at first glance. The API can be used by hand, calling two SQL functions. I have trained some hundreds of administrators, and they could follow. > But then it's futile to discuss with religious people, as they are > blind to reasoning: AL II. 58, "The slaves shall serve." Suspicion becomes certainty: You are not out to understand, but to troll. Bye. Laurenz Albe