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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2016-08-07 14:36:02 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2016-08-07 14:36:02 -0400 |
| commit | 07a601eedab7c5fa4d62055fa3efacef2f38e446 (patch) | |
| tree | a7cff4ff9db946e5f061b99e3c00cfce2f9dba4b /src | |
| parent | bcbecbce2fde3c6dfa9080db11663877808a007d (diff) | |
| download | postgresql-07a601eedab7c5fa4d62055fa3efacef2f38e446.tar.gz postgresql-07a601eedab7c5fa4d62055fa3efacef2f38e446.zip | |
Avoid crashing in GetOldestSnapshot() if there are no known snapshots.
The sole caller expects NULL to be returned in such a case, so make
it so and document it.
Per reports from Andreas Seltenreich and Regina Obe. This doesn't
really fix their problem, as now their RETURNING queries will say
"ERROR: no known snapshots", but in any case this function should
not dump core in a reasonably-foreseeable situation.
Report: <87vazemeda.fsf@credativ.de>
Report: <20160807051854.1427.32414@wrigleys.postgresql.org>
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/utils/time/snapmgr.c | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c index 4bddaed33ba..1ec9f70f0ee 100644 --- a/src/backend/utils/time/snapmgr.c +++ b/src/backend/utils/time/snapmgr.c @@ -399,14 +399,14 @@ GetLatestSnapshot(void) /* * GetOldestSnapshot * - * Get the oldest known snapshot, as judged by the LSN. + * Get the transaction's oldest known snapshot, as judged by the LSN. + * Will return NULL if there are no active or registered snapshots. */ Snapshot GetOldestSnapshot(void) { Snapshot OldestRegisteredSnapshot = NULL; XLogRecPtr RegisteredLSN = InvalidXLogRecPtr; - XLogRecPtr ActiveLSN = InvalidXLogRecPtr; if (!pairingheap_is_empty(&RegisteredSnapshots)) { @@ -416,10 +416,12 @@ GetOldestSnapshot(void) } if (OldestActiveSnapshot != NULL) - ActiveLSN = OldestActiveSnapshot->as_snap->lsn; + { + XLogRecPtr ActiveLSN = OldestActiveSnapshot->as_snap->lsn; - if (XLogRecPtrIsInvalid(RegisteredLSN) || RegisteredLSN > ActiveLSN) - return OldestActiveSnapshot->as_snap; + if (XLogRecPtrIsInvalid(RegisteredLSN) || RegisteredLSN > ActiveLSN) + return OldestActiveSnapshot->as_snap; + } return OldestRegisteredSnapshot; } |