I just noticed that if track_commit_timestamp is enabled, the
oldestCommitTsXid and newestCommitTsXid don't persist after a server
restart, so you can't ask for the commit ts of a transaction that
committed before the last server start, although the information is
still available (unless of course if a freeze occured). AFAICT it
always behave this way.
I'm not familiar with that code, but it looks like these counters are
supposed to be restored in StartupXLOG(), with a call to
SetCommitTsLimit(). However, this function doesn't store the new value
if ShmemVariableCache->oldestCommitTsXid is InvalidTransactionId, which
is the initial value.
So the counters are initialized on a subsequent call of
ActivateCommitTs(), which does:
if (ShmemVariableCache->oldestCommitTsXid == InvalidTransactionId)
{
ShmemVariableCache->oldestCommitTsXid =
ShmemVariableCache->newestCommitTsXid =
ReadNewTransactionId();
}
(but doesn't try to cleanup the SLRU directory btw)
leaving any previous transaction unreachable. Simple attached patch
seems to fix the issue. I tried on a master and a replica, enabling and
disabling track_commit_timestamp, and everything seemed to work as intended.
--
Julien Rouhaud
http://dalibo.com - http://dalibo.org
diff --git a/src/backend/access/transam/commit_ts.c b/src/backend/access/transam/commit_ts.c
index a8d275f..7746578 100644
--- a/src/backend/access/transam/commit_ts.c
+++ b/src/backend/access/transam/commit_ts.c
@@ -844,6 +844,8 @@ SetCommitTsLimit(TransactionId oldestXact, TransactionId newestXact)
else
{
Assert(ShmemVariableCache->newestCommitTsXid == InvalidTransactionId);
+ ShmemVariableCache->oldestCommitTsXid = oldestXact;
+ ShmemVariableCache->newestCommitTsXid = newestXact;
}
LWLockRelease(CommitTsLock);
}
--
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