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Fix wrong logic in TransactionIdInRecentPast()

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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
This commit is contained in:
Alexander Korotkov 2024-02-08 12:45:26 +02:00
parent d17a3a4c6a
commit 503299b7f7
1 changed files with 19 additions and 11 deletions
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30
src/backend/utils/adt/xid8funcs.c
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@ -90,11 +90,12 @@ typedef struct
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);
@ -127,17 +128,24 @@ 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
* ShmemVariableCache->oldestClogXid to determine whether the relevant
* CLOG entry is guaranteed to still exist.
* If fxid is not older than ShmemVariableCache->oldestClogXid, the
* relevant CLOG entry is guaranteed to still exist. Convert
* ShmemVariableCache->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, ShmemVariableCache->oldestClogXid))
return false;
return true;
oldest_xid = ShmemVariableCache->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);
}
/*