diff options
| -rw-r--r-- | src/backend/utils/time/snapmgr.c | 20 |
1 files changed, 16 insertions, 4 deletions
diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c index 9d02f7638b8..85b5d5cdb9e 100644 --- a/src/backend/utils/time/snapmgr.c +++ b/src/backend/utils/time/snapmgr.c @@ -983,24 +983,36 @@ GetFullRecentGlobalXmin(void) uint32 nextxid_epoch; TransactionId nextxid_xid; uint32 epoch; + TransactionId horizon = RecentGlobalXmin; - Assert(TransactionIdIsNormal(RecentGlobalXmin)); + Assert(TransactionIdIsNormal(horizon)); /* * Compute the epoch from the next XID's epoch. This relies on the fact * that RecentGlobalXmin must be within the 2 billion XID horizon from the * next XID. + * + * Need to be careful to prevent wrapping around during epoch 0, otherwise + * we would generate an xid far into the future when converting to a + * FullTransactionId. This can happen because RecentGlobalXmin can be held + * back via vacuum_defer_cleanup_age. */ nextxid_full = ReadNextFullTransactionId(); nextxid_epoch = EpochFromFullTransactionId(nextxid_full); nextxid_xid = XidFromFullTransactionId(nextxid_full); - if (RecentGlobalXmin > nextxid_xid) + if (horizon <= nextxid_xid) + epoch = nextxid_epoch; + else if (nextxid_epoch > 0) epoch = nextxid_epoch - 1; else - epoch = nextxid_epoch; + { + /* don't wrap around */ + epoch = 0; + horizon = FirstNormalTransactionId; + } - return FullTransactionIdFromEpochAndXid(epoch, RecentGlobalXmin); + return FullTransactionIdFromEpochAndXid(epoch, horizon); } /* |