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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2016-05-24 15:20:12 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2016-05-24 15:20:12 -0400 |
| commit | a34c3dd50f661126ac51c794e63f7932fe657542 (patch) | |
| tree | 8f03169bec40c127b2062e47a16c8e48797aa16d | |
| parent | e504d915bbf352ecfc4ed335af934e799bf01053 (diff) | |
| download | postgresql-a34c3dd50f661126ac51c794e63f7932fe657542.tar.gz postgresql-a34c3dd50f661126ac51c794e63f7932fe657542.zip | |
Avoid consuming an XID during vac_truncate_clog().
vac_truncate_clog() uses its own transaction ID as the comparison point in
a sanity check that no database's datfrozenxid has already wrapped around
"into the future". That was probably fine when written, but in a lazy
vacuum we won't have assigned an XID, so calling GetCurrentTransactionId()
causes an XID to be assigned when otherwise one would not be. Most of the
time that's not a big problem ... but if we are hard up against the
wraparound limit, consuming XIDs during antiwraparound vacuums is a very
bad thing.
Instead, use ReadNewTransactionId(), which not only avoids this problem
but is in itself a better comparison point to test whether wraparound
has already occurred.
Report and patch by Alexander Korotkov. Back-patch to all versions.
Report: <CAPpHfdspOkmiQsxh-UZw2chM6dRMwXAJGEmmbmqYR=yvM7-s6A@mail.gmail.com>
| -rw-r--r-- | src/backend/commands/vacuum.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c index be89b9b86b6..9759ae11a97 100644 --- a/src/backend/commands/vacuum.c +++ b/src/backend/commands/vacuum.c @@ -1050,7 +1050,7 @@ vac_truncate_clog(TransactionId frozenXID, TransactionId lastSaneFrozenXid, MultiXactId lastSaneMinMulti) { - TransactionId myXID = GetCurrentTransactionId(); + TransactionId nextXID = ReadNewTransactionId(); Relation relation; HeapScanDesc scan; HeapTuple tuple; @@ -1099,7 +1099,7 @@ vac_truncate_clog(TransactionId frozenXID, MultiXactIdPrecedes(lastSaneMinMulti, dbform->datminmxid)) bogus = true; - if (TransactionIdPrecedes(myXID, dbform->datfrozenxid)) + if (TransactionIdPrecedes(nextXID, dbform->datfrozenxid)) frozenAlreadyWrapped = true; else if (TransactionIdPrecedes(dbform->datfrozenxid, frozenXID)) { |