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Commitd44060c

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Fix wrong logic in TransactionIdInRecentPast()
The TransactionIdInRecentPast() should return false for all the transactionsolder than TransamVariables->oldestClogXid. However, the function containsa bug in comparison FullTransactionId to TransactionID allowing fulltransactions between nextXid - 2^32 and oldestClogXid - 2^31.This commit fixes TransactionIdInRecentPast() by turning the oldestClogXid intoFullTransactionId first, then performing the comparison.Backpatch to all supported versions.Reported-by: Egor ChindyaskinBug: 18212Discussion:https://postgr.es/m/18212-547307f8adf57262%40postgresql.orgAuthor: Karina LitskevichReviewed-by: Kyotaro HoriguchiBackpatch-through: 12
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1 file changed

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‎src/backend/utils/adt/txid.c

Lines changed: 21 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -116,10 +116,14 @@ TransactionIdInRecentPast(uint64 xid_with_epoch, TransactionId *extracted_xid)
116116
{
117117
uint32xid_epoch= (uint32) (xid_with_epoch >>32);
118118
TransactionIdxid= (TransactionId)xid_with_epoch;
119+
FullTransactionIdfxid;
119120
uint32now_epoch;
120121
TransactionIdnow_epoch_next_xid;
121122
FullTransactionIdnow_fullxid;
123+
TransactionIdoldest_xid;
124+
FullTransactionIdoldest_fxid;
122125

126+
fxid=FullTransactionIdFromEpochAndXid(xid_epoch,xid);
123127
now_fullxid=ReadNextFullTransactionId();
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now_epoch_next_xid=XidFromFullTransactionId(now_fullxid);
125129
now_epoch=EpochFromFullTransactionId(now_fullxid);
@@ -151,17 +155,24 @@ TransactionIdInRecentPast(uint64 xid_with_epoch, TransactionId *extracted_xid)
151155
Assert(LWLockHeldByMe(CLogTruncationLock));
152156

153157
/*
154-
* If the transaction ID has wrapped around, it's definitely too old to
155-
* determine the commit status. Otherwise, we can compare it to
156-
* ShmemVariableCache->oldestClogXid to determine whether the relevant
157-
* CLOG entry is guaranteed to still exist.
158+
* If fxid is not older than ShmemVariableCache->oldestClogXid, the
159+
* relevant CLOG entry is guaranteed to still exist. Convert
160+
* ShmemVariableCache->oldestClogXid into a FullTransactionId to compare
161+
* it with fxid. Determine the right epoch knowing that oldest_fxid
162+
* shouldn't be more than 2^31 older than now_fullxid.
158163
*/
159-
if (xid_epoch+1<now_epoch
160-
|| (xid_epoch+1==now_epoch&&xid<now_epoch_next_xid)
161-
||TransactionIdPrecedes(xid,ShmemVariableCache->oldestClogXid))
162-
return false;
163-
164-
return true;
164+
oldest_xid=ShmemVariableCache->oldestClogXid;
165+
Assert(TransactionIdPrecedesOrEquals(oldest_xid,now_epoch_next_xid));
166+
if (oldest_xid <=now_epoch_next_xid)
167+
{
168+
oldest_fxid=FullTransactionIdFromEpochAndXid(now_epoch,oldest_xid);
169+
}
170+
else
171+
{
172+
Assert(now_epoch>0);
173+
oldest_fxid=FullTransactionIdFromEpochAndXid(now_epoch-1,oldest_xid);
174+
}
175+
return !FullTransactionIdPrecedes(fxid,oldest_fxid);
165176
}
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167178
/*

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