Re: Incorrect snapshots while promoting hot standby node when 2PC is used

Andres Freund <andres@anarazel.de> writes:
> Michael Paquier (running locally I think), and subsequently Thomas Munro
> (noticing [1]), privately reported that they noticed an assertion failure in
> GetSnapshotData(). Both reasonably were wondering if that's related to the
> snapshot scalability patches.
> Michael reported the following assertion failure in 023_pitr_prepared_xact.pl:
>> TRAP: FailedAssertion("TransactionIdPrecedesOrEquals(TransactionXmin, RecentXmin)", File: "procarray.c", Line: 2468,
PID:22901) 

mantid just showed a failure that looks like the same thing, at
least it's also in 023_pitr_prepared_xact.pl:

https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=mantid&dt=2021-05-03%2013%3A07%3A06

The assertion line number is rather different though:

TRAP: FailedAssertion("TransactionIdPrecedesOrEquals(TransactionXmin, RecentXmin)", File: "procarray.c", Line: 2094,
PID:1163004) 

and interestingly, this happened in a parallel worker:

postgres: node_pitr: parallel worker for PID 1162998 (ExceptionalCondition+0x7a)[0x946eca]
postgres: node_pitr: parallel worker for PID 1162998 (GetSnapshotData+0x897)[0x7ef327]
postgres: node_pitr: parallel worker for PID 1162998 (GetNonHistoricCatalogSnapshot+0x4a)[0x986a5a]
postgres: node_pitr: parallel worker for PID 1162998 (systable_beginscan+0x189)[0x4fffe9]
postgres: node_pitr: parallel worker for PID 1162998 [0x937336]
postgres: node_pitr: parallel worker for PID 1162998 [0x937743]
postgres: node_pitr: parallel worker for PID 1162998 (RelationIdGetRelation+0x85)[0x93f155]
postgres: node_pitr: parallel worker for PID 1162998 (relation_open+0x5c)[0x4a348c]
postgres: node_pitr: parallel worker for PID 1162998 (index_open+0x6)[0x5007a6]
postgres: node_pitr: parallel worker for PID 1162998 (systable_beginscan+0x177)[0x4fffd7]
postgres: node_pitr: parallel worker for PID 1162998 [0x937336]
postgres: node_pitr: parallel worker for PID 1162998 [0x93e1c1]
postgres: node_pitr: parallel worker for PID 1162998 (RelationIdGetRelation+0xbd)[0x93f18d]
postgres: node_pitr: parallel worker for PID 1162998 (relation_open+0x5c)[0x4a348c]
postgres: node_pitr: parallel worker for PID 1162998 (table_open+0x6)[0x532656]
postgres: node_pitr: parallel worker for PID 1162998 [0x937306]
postgres: node_pitr: parallel worker for PID 1162998 [0x93e1c1]
postgres: node_pitr: parallel worker for PID 1162998 (RelationIdGetRelation+0xbd)[0x93f18d]
postgres: node_pitr: parallel worker for PID 1162998 (relation_open+0x5c)[0x4a348c]
postgres: node_pitr: parallel worker for PID 1162998 (table_open+0x6)[0x532656]
postgres: node_pitr: parallel worker for PID 1162998 [0x92c4f1]
postgres: node_pitr: parallel worker for PID 1162998 (SearchCatCache1+0x176)[0x92e236]
postgres: node_pitr: parallel worker for PID 1162998 (TupleDescInitEntry+0xb3)[0x4a7eb3]
postgres: node_pitr: parallel worker for PID 1162998 [0x688f30]
postgres: node_pitr: parallel worker for PID 1162998 (ExecInitResultTupleSlotTL+0x1b)[0x68a8fb]
postgres: node_pitr: parallel worker for PID 1162998 (ExecInitResult+0x92)[0x6af902]
postgres: node_pitr: parallel worker for PID 1162998 (ExecInitNode+0x446)[0x684b06]
postgres: node_pitr: parallel worker for PID 1162998 (standard_ExecutorStart+0x269)[0x67d7b9]
postgres: node_pitr: parallel worker for PID 1162998 (ParallelQueryMain+0x1a3)[0x681d83]
postgres: node_pitr: parallel worker for PID 1162998 (ParallelWorkerMain+0x408)[0x53c218]
postgres: node_pitr: parallel worker for PID 1162998 (StartBackgroundWorker+0x23f)[0x774ebf]
postgres: node_pitr: parallel worker for PID 1162998 [0x780f3d]

            regards, tom lane