Обсуждение: Online backup vs Continuous backup
I noticed that we are using the term "Online Backup" in our documentation when we are talking about continuous backup and PITR. To me, "online backup" is doing a backup while the system is online (online-backup), and that is accomplished by pg_dump. I know a lot of databases us "Online Backup" but I assume this is for historical reasons because at some time in the past their full backups didn't work while the database was online. Other systems use the term "Continuous Logging", but I think that is too easily confused with the server activity logs. I suggest the following patch to rename our capability "Continuous Backup". -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 Index: backup.sgml =================================================================== RCS file: /cvsroot/pgsql/doc/src/sgml/backup.sgml,v retrieving revision 2.76 diff -c -r2.76 backup.sgml *** backup.sgml 7 Nov 2005 17:36:44 -0000 2.76 --- backup.sgml 26 Dec 2005 16:30:48 -0000 *************** *** 19,25 **** <itemizedlist> <listitem><para><acronym>SQL</> dump</para></listitem> <listitem><para>File system level backup</para></listitem> ! <listitem><para>On-line backup</para></listitem> </itemizedlist> Each has its own strengths and weaknesses. </para> --- 19,25 ---- <itemizedlist> <listitem><para><acronym>SQL</> dump</para></listitem> <listitem><para>File system level backup</para></listitem> ! <listitem><para>Continuous backup</para></listitem> </itemizedlist> Each has its own strengths and weaknesses. </para> *************** *** 373,382 **** </sect1> <sect1 id="backup-online"> ! <title>On-line backup and point-in-time recovery (PITR)</title> <indexterm zone="backup"> ! <primary>on-line backup</primary> </indexterm> <indexterm zone="backup"> --- 373,382 ---- </sect1> <sect1 id="backup-online"> ! <title>Continuous backup and point-in-time recovery (PITR)</title> <indexterm zone="backup"> ! <primary>continuous backup</primary> </indexterm> <indexterm zone="backup"> *************** *** 452,458 **** </para> <para> ! To recover successfully using an on-line backup, you need a continuous sequence of archived WAL files that extends back at least as far as the start time of your backup. So to get started, you should set up and test your procedure for archiving WAL files <emphasis>before</> you take your --- 452,458 ---- </para> <para> ! To recover successfully using a continuous backup, you need a continuous sequence of archived WAL files that extends back at least as far as the start time of your backup. So to get started, you should set up and test your procedure for archiving WAL files <emphasis>before</> you take your *************** *** 782,793 **** <function>pg_start_backup</> or <function>pg_stop_backup</>, and you will therefore be left to your own devices to keep track of which backup dump is which and how far back the associated WAL files go. ! It is generally better to follow the on-line backup procedure above. </para> </sect2> <sect2 id="backup-pitr-recovery"> ! <title>Recovering with an On-line Backup</title> <para> Okay, the worst has happened and you need to recover from your backup. --- 782,793 ---- <function>pg_start_backup</> or <function>pg_stop_backup</>, and you will therefore be left to your own devices to keep track of which backup dump is which and how far back the associated WAL files go. ! It is generally better to follow the continuous backup procedure above. </para> </sect2> <sect2 id="backup-pitr-recovery"> ! <title>Recovering with a Continuous Backup</title> <para> Okay, the worst has happened and you need to recover from your backup. *************** *** 1123,1129 **** <title>Caveats</title> <para> ! At this writing, there are several limitations of the on-line backup technique. These will probably be fixed in future releases: <itemizedlist> --- 1123,1129 ---- <title>Caveats</title> <para> ! At this writing, there are several limitations of the continuous backup technique. These will probably be fixed in future releases: <itemizedlist>
Bruce Momjian <pgman@candle.pha.pa.us> writes: > I suggest the following patch to rename our capability "Continuous > Backup". This doesn't seem like an improvement. "Online backup" is the standard terminology AFAIK. regards, tom lane
Tom Lane wrote: > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > I suggest the following patch to rename our capability "Continuous > > Backup". > > This doesn't seem like an improvement. "Online backup" is the standard > terminology AFAIK. But why is it the standard terminology? It doesn't seem logical. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
Bruce Momjian wrote: > I noticed that we are using the term "Online Backup" in our > documentation when we are talking about continuous backup and PITR. > > To me, "online backup" is doing a backup while the system is online > (online-backup), and that is accomplished by pg_dump. I know a lot of > databases us "Online Backup" but I assume this is for historical reasons > because at some time in the past their full backups didn't work while > the database was online. Other systems use the term "Continuous > Logging", but I think that is too easily confused with the server > activity logs. > > I suggest the following patch to rename our capability "Continuous > Backup". I have never heard the term Continuous backup. Although I have heard online backup. The problem is that when I hear the term online backup I think Hot backup which is what we do with pg_dump. I would just call the other Point in time recovery :) > >
Joshua D. Drake wrote: > Bruce Momjian wrote: > > I noticed that we are using the term "Online Backup" in our > > documentation when we are talking about continuous backup and PITR. > > > > To me, "online backup" is doing a backup while the system is online > > (online-backup), and that is accomplished by pg_dump. I know a lot of > > databases us "Online Backup" but I assume this is for historical reasons > > because at some time in the past their full backups didn't work while > > the database was online. Other systems use the term "Continuous > > Logging", but I think that is too easily confused with the server > > activity logs. > > > > I suggest the following patch to rename our capability "Continuous > > Backup". > > I have never heard the term Continuous backup. Although I have heard > online backup. The problem is that when I hear the term online backup > I think Hot backup which is what we do with pg_dump. Yes, that is my problem too. > I would just call the other Point in time recovery :) The problem there is that it is "recovery", and the documentation talks about the "backup" step. I am thinking we are going to have to add something like "Continuous backup, also called Online Backup" or something like that. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
Am Montag, 26. Dezember 2005 20:46 schrieb Heikki Linnakangas: > FWIW, I believe "log archival" is a common term for that. I like that better, although there are a lot of logs, so maybe "transaction log archival". Considering the list originally referenced: - File system backup - SQL dump - (Transaction log archival?) This addresses the technical workings of the various backup systems. The fact that it is or isn't on-line, hot, continuous, fast, or flexible is secondary.
Peter Eisentraut wrote: > Am Montag, 26. Dezember 2005 20:46 schrieb Heikki Linnakangas: > > FWIW, I believe "log archival" is a common term for that. > > I like that better, although there are a lot of logs, so maybe > "transaction log archival". Yep, when I think of log archiving, I think of saving the server logs, which thanks to log file rotation, we kind of support. The problem is that when I think of the transaction log, I think of clog because it is the transaction status log. :-( I am thinking anything that says "log" is going to be confusing. How about "Transaction Archiving"? > Considering the list originally referenced: > > - File system backup - SQL dump - (Transaction log archival?) > > This addresses the technical workings of the various backup systems. > The fact that it is or isn't on-line, hot, continuous, fast, or flexible > is secondary. To me, the continuous activity is the significant feature of that backup method. I chose "Continuous Backup" because it is the continual activity that is significant. "Continuous Archiving"? -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
Bruce Momjian <pgman@candle.pha.pa.us> writes: >> This addresses the technical workings of the various backup systems. >> The fact that it is or isn't on-line, hot, continuous, fast, or flexible >> is secondary. > To me, the continuous activity is the significant feature of that backup > method. I chose "Continuous Backup" because it is the continual > activity that is significant. "Continuous Archiving"? I like Peter's suggestion as-is; or "WAL Archiving". I don't like applying adjectives that are not specific to the particular method. That will just create more confusion down the road if we add another feature that could also be called "continuous archiving". regards, tom lane
On Mon, 2005-12-26 at 13:46 -0500, Bruce Momjian wrote: > Tom Lane wrote: > > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > > I suggest the following patch to rename our capability "Continuous > > > Backup". > > > > This doesn't seem like an improvement. "Online backup" is the standard > > terminology AFAIK. > > But why is it the standard terminology? It doesn't seem logical. Well, as Greg says its a physical backup that can be done on-line, so online backup makes perfect sense to me. I've never had somebody say "that makes no sense" before. Nomenclature is different everywhere, I accept. I generally describe it like this: Logical Backup - use pg_dump - must be done on-line Physical Backup All file copy only - must be Cold/Off-line backup All file copy + WAL archiving - allows Hot/Online or Cold/Offline backup People understand those terms... When do I mention PITR? Well, I describe this as Archive Recovery, with an option to go to end-of-logs, or to a point-in-time. [In the code, the mode variable is InArchiveRecovery.] I do think that saying "do you use PITR?" makes little sense. We should be talking about the backup mode, not the potential future recovery mode. I think it would all make more sense if we described the use of archive_command = something as being in "WAL Archive Mode". That would then allow us to say: "You can only take Online Backups while in WAL Archive Mode". "If you ever wish to perform PITR, you must use WAL Archive Mode". "If you backed-up in WAL Archive Mode, you can perform an Archive Recovery". Best Regards, Simon Riggs
On Mon, 26 Dec 2005, Bruce Momjian wrote: > Joshua D. Drake wrote: > >> I have never heard the term Continuous backup. Although I have heard >> online backup. The problem is that when I hear the term online backup >> I think Hot backup which is what we do with pg_dump. > > Yes, that is my problem too. > >> I would just call the other Point in time recovery :) > > The problem there is that it is "recovery", and the documentation talks > about the "backup" step. I am thinking we are going to have to add > something like "Continuous backup, also called Online Backup" or > something like that. FWIW, I believe "log archival" is a common term for that. - Heikki
Bruce Momjian <pgman@candle.pha.pa.us> writes: > I noticed that we are using the term "Online Backup" in our > documentation when we are talking about continuous backup and PITR. > > To me, "online backup" is doing a backup while the system is online > (online-backup), and that is accomplished by pg_dump. Well fwiw what pg_dump does isn't even considered a "backup" at all in other systems. It's a "logical export" or something of that sort. It's not considered a "backup" because it's saving something different than the actual physical database. When you restore you get something (hopefully) logically equivalent but still physically different. Hot backups which is what you read "online backup" to mean is pretty closely tied to PITR log archiving backups. One isn't very useful without the other. Specifically, you can have all the archived logs in the world but if you don't have a backup to start from they're useless. And in postgres I gather hot backups aren't very useful if you don't have the transaction logs necessary to fix any torn pages. -- greg
> Bruce Momjian <pgman@candle.pha.pa.us> writes: >> I suggest the following patch to rename our capability "Continuous >> Backup". > > This doesn't seem like an improvement. "Online backup" is the standard > terminology AFAIK. There's something ambiguous about it, in view that there are two useful points in time for a backup to be "as of," namely: a) The start time (which is what pg_dump does), and b) The end time (which I believe is not uncommon with other systems). PITR is obviously more like b)... -- wm(X,Y):-write(X),write('@'),write(Y). wm('cbbrowne','gmail.com'). http://linuxfinances.info/info/slony.html Keeping instructions and operands in different memories saves .20 (.09) microseconds.
Tom Lane wrote: > Bruce Momjian <pgman@candle.pha.pa.us> writes: > >> This addresses the technical workings of the various backup systems. > >> The fact that it is or isn't on-line, hot, continuous, fast, or flexible > >> is secondary. > > > To me, the continuous activity is the significant feature of that backup > > method. I chose "Continuous Backup" because it is the continual > > activity that is significant. "Continuous Archiving"? > > I like Peter's suggestion as-is; or "WAL Archiving". I don't like > applying adjectives that are not specific to the particular method. > That will just create more confusion down the road if we add another > feature that could also be called "continuous archiving". I do like "WAL Archiving" but I am concerned that it references a specific internal implementation detail (WAL). Is that OK? Also, I am concerned that is specificially talks about archiving the wal files and is not general enough to include the file system backup that is also necessary. -- Bruce Momjian http://candle.pha.pa.us SRA OSS, Inc. http://www.sraoss.com + If your life is a hard drive, Christ can be your backup. +