Fix wrong logic in TransactionIdInRecentPast()
The TransactionIdInRecentPast() should return false for all the transactions older than TransamVariables->oldestClogXid. However, the function contains a bug in comparison FullTransactionId to TransactionID allowing full transactions between nextXid - 2^32 and oldestClogXid - 2^31. This commit fixes TransactionIdInRecentPast() by turning the oldestClogXid into FullTransactionId first, then performing the comparison. Backpatch to all supported versions. Reported-by: Egor Chindyaskin Bug: 18212 Discussion: https://postgr.es/m/18212-547307f8adf57262%40postgresql.org Author: Karina Litskevich Reviewed-by: Kyotaro Horiguchi Backpatch-through: 12
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@ -98,11 +98,12 @@ StaticAssertDecl(MAX_BACKENDS * 2 <= PG_SNAPSHOT_MAX_NXIP,
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static bool
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TransactionIdInRecentPast(FullTransactionId fxid, TransactionId *extracted_xid)
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{
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uint32 xid_epoch = EpochFromFullTransactionId(fxid);
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TransactionId xid = XidFromFullTransactionId(fxid);
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uint32 now_epoch;
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TransactionId now_epoch_next_xid;
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FullTransactionId now_fullxid;
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TransactionId oldest_xid;
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FullTransactionId oldest_fxid;
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now_fullxid = ReadNextFullTransactionId();
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now_epoch_next_xid = XidFromFullTransactionId(now_fullxid);
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@ -135,17 +136,24 @@ TransactionIdInRecentPast(FullTransactionId fxid, TransactionId *extracted_xid)
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Assert(LWLockHeldByMe(XactTruncationLock));
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/*
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* If the transaction ID has wrapped around, it's definitely too old to
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* determine the commit status. Otherwise, we can compare it to
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* TransamVariables->oldestClogXid to determine whether the relevant CLOG
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* entry is guaranteed to still exist.
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* If fxid is not older than TransamVariables->oldestClogXid, the relevant
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* CLOG entry is guaranteed to still exist. Convert
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* TransamVariables->oldestClogXid into a FullTransactionId to compare it
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* with fxid. Determine the right epoch knowing that oldest_fxid
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* shouldn't be more than 2^31 older than now_fullxid.
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*/
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if (xid_epoch + 1 < now_epoch
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|| (xid_epoch + 1 == now_epoch && xid < now_epoch_next_xid)
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|| TransactionIdPrecedes(xid, TransamVariables->oldestClogXid))
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return false;
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return true;
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oldest_xid = TransamVariables->oldestClogXid;
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Assert(TransactionIdPrecedesOrEquals(oldest_xid, now_epoch_next_xid));
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if (oldest_xid <= now_epoch_next_xid)
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{
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oldest_fxid = FullTransactionIdFromEpochAndXid(now_epoch, oldest_xid);
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}
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else
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{
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Assert(now_epoch > 0);
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oldest_fxid = FullTransactionIdFromEpochAndXid(now_epoch - 1, oldest_xid);
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}
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return !FullTransactionIdPrecedes(fxid, oldest_fxid);
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}
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/*
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