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| author | Thomas Munro <tmunro@postgresql.org> | 2020-03-12 18:06:54 +1300 |
|---|---|---|
| committer | Thomas Munro <tmunro@postgresql.org> | 2020-03-12 18:06:54 +1300 |
| commit | a493f933422c97f40584efbd07c3e6884ed3ace3 (patch) | |
| tree | b337ef41ccb3b7c4253f9b63d78427271a55a136 | |
| parent | 13f353b0e0775642c212ac557b371eefa171d179 (diff) | |
| download | postgresql-a493f933422c97f40584efbd07c3e6884ed3ace3.tar.gz postgresql-a493f933422c97f40584efbd07c3e6884ed3ace3.zip | |
Fix nextXid tracking bug on standbys (9.5-11 only).
RecordKnownAssignedTransactionIds() should never move
nextXid backwards. Before this commit, that could happen
if some other code path had advanced it without advancing
latestObservedXid.
One consequence is that a well timed XLOG_CHECKPOINT_ONLINE
could cause hot standby feedback messages to get confused
and report an xmin from a future epoch, potentially allowing
vacuum to run too soon on the primary.
Repair, by making sure RecordKnownAssignedTransactionIds()
can only move nextXid forwards.
In release 12 and master, this was already done by commit
2fc7af5e, which consolidated similar code and straightened
out this bug. Back-patch to supported releases before that.
Author: Eka Palamadai <ekanatha@amazon.com>
Discussion: https://postgr.es/m/98BB4805-D0A2-48E1-96F4-15014313EADC@amazon.com
| -rw-r--r-- | src/backend/storage/ipc/procarray.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c index ddd3461d56e..50b9aea6838 100644 --- a/src/backend/storage/ipc/procarray.c +++ b/src/backend/storage/ipc/procarray.c @@ -3256,7 +3256,8 @@ RecordKnownAssignedTransactionIds(TransactionId xid) next_expected_xid = latestObservedXid; TransactionIdAdvance(next_expected_xid); LWLockAcquire(XidGenLock, LW_EXCLUSIVE); - ShmemVariableCache->nextXid = next_expected_xid; + if (TransactionIdFollows(next_expected_xid, ShmemVariableCache->nextXid)) + ShmemVariableCache->nextXid = next_expected_xid; LWLockRelease(XidGenLock); } } |