index be5e28c93ab77940afcc36d30602ae78dd71d291..aa64a7c8b3fc4d1fcd123b762642f6d0509f86ca 100644 (file)
@@ -98,11 +98,12 @@ StaticAssertDecl(MAX_BACKENDS * 2 <= PG_SNAPSHOT_MAX_NXIP,
static bool
TransactionIdInRecentPast(FullTransactionId fxid, TransactionId *extracted_xid)
{
- uint32 xid_epoch = EpochFromFullTransactionId(fxid);
TransactionId xid = XidFromFullTransactionId(fxid);
uint32 now_epoch;
TransactionId now_epoch_next_xid;
FullTransactionId now_fullxid;
+ TransactionId oldest_xid;
+ FullTransactionId oldest_fxid;
now_fullxid = ReadNextFullTransactionId();
now_epoch_next_xid = XidFromFullTransactionId(now_fullxid);
@@ -135,17 +136,24 @@ TransactionIdInRecentPast(FullTransactionId fxid, TransactionId *extracted_xid)
Assert(LWLockHeldByMe(XactTruncationLock));
/*
- * If the transaction ID has wrapped around, it's definitely too old to
- * determine the commit status. Otherwise, we can compare it to
- * TransamVariables->oldestClogXid to determine whether the relevant CLOG
- * entry is guaranteed to still exist.
+ * If fxid is not older than TransamVariables->oldestClogXid, the relevant
+ * CLOG entry is guaranteed to still exist. Convert
+ * TransamVariables->oldestClogXid into a FullTransactionId to compare it
+ * with fxid. Determine the right epoch knowing that oldest_fxid
+ * shouldn't be more than 2^31 older than now_fullxid.
*/
- if (xid_epoch + 1 < now_epoch
- || (xid_epoch + 1 == now_epoch && xid < now_epoch_next_xid)
- || TransactionIdPrecedes(xid, TransamVariables->oldestClogXid))
- return false;
-
- return true;
+ oldest_xid = TransamVariables->oldestClogXid;
+ Assert(TransactionIdPrecedesOrEquals(oldest_xid, now_epoch_next_xid));
+ if (oldest_xid <= now_epoch_next_xid)
+ {
+ oldest_fxid = FullTransactionIdFromEpochAndXid(now_epoch, oldest_xid);
+ }
+ else
+ {
+ Assert(now_epoch > 0);
+ oldest_fxid = FullTransactionIdFromEpochAndXid(now_epoch - 1, oldest_xid);
+ }
+ return !FullTransactionIdPrecedes(fxid, oldest_fxid);
}
/*