GetSnapshotData() set TransactionXmin = MyProc->xmin, but when
SnapshotResetXmin() advanced MyProc->xmin, it did not advance
TransactionXmin correspondingly. That meant that TransactionXmin could
be older than MyProc->xmin, and XIDs between than TransactionXmin and
the real MyProc->xmin could be vacuumed away. One known consequence is
in pg_subtrans lookups: we might try to look up the status of an XID
that was already truncated away.
Back-patch to all supported versions.
Reviewed-by: Andres Freund
Discussion: https://www.postgresql.org/message-id/
d27a046d-a1e4-47d1-a95c-
fbabe41debb4@iki.fi
index e60360338d5750654f13093b0d5e10ddb26ecea1..e002d0c1368d22eb0929765c8059901c7d7ac50c 100644 (file)
if (pairingheap_is_empty(&RegisteredSnapshots))
{
- MyProc->xmin = InvalidTransactionId;
+ MyProc->xmin = TransactionXmin = InvalidTransactionId;
return;
}
pairingheap_first(&RegisteredSnapshots));
if (TransactionIdPrecedes(MyProc->xmin, minSnapshot->xmin))
- MyProc->xmin = minSnapshot->xmin;
+ MyProc->xmin = TransactionXmin = minSnapshot->xmin;
}
/*