diff options
| author | Tom Lane | 2016-05-24 19:20:12 +0000 |
|---|---|---|
| committer | Tom Lane | 2016-05-24 19:20:12 +0000 |
| commit | 2e7f0c34aa6dd2f4c02f57d9dd5c37eeeb661198 (patch) | |
| tree | 090ca196a58c99e5697cc9128a8e3ab608f42a3f /src | |
| parent | fca2eb3d43226cb119b682fda7716c5a4c28a841 (diff) | |
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>
Diffstat (limited to 'src')
| -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 a5235148d49..c019b7230bf 100644 --- a/src/backend/commands/vacuum.c +++ b/src/backend/commands/vacuum.c @@ -802,7 +802,7 @@ vac_update_datfrozenxid(void) static void vac_truncate_clog(TransactionId frozenXID) { - TransactionId myXID = GetCurrentTransactionId(); + TransactionId nextXID = ReadNewTransactionId(); Relation relation; HeapScanDesc scan; HeapTuple tuple; @@ -834,7 +834,7 @@ vac_truncate_clog(TransactionId frozenXID) Assert(TransactionIdIsNormal(dbform->datfrozenxid)); - if (TransactionIdPrecedes(myXID, dbform->datfrozenxid)) + if (TransactionIdPrecedes(nextXID, dbform->datfrozenxid)) frozenAlreadyWrapped = true; else if (TransactionIdPrecedes(dbform->datfrozenxid, frozenXID)) { |