From 503299b7f728409874adc2f5df9d42857700b046 Mon Sep 17 00:00:00 2001 From: Alexander Korotkov Date: Thu, 8 Feb 2024 12:45:26 +0200 Subject: [PATCH] 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 --- src/backend/utils/adt/xid8funcs.c | 30 +++++++++++++++++++----------- 1 file changed, 19 insertions(+), 11 deletions(-) diff --git a/src/backend/utils/adt/xid8funcs.c b/src/backend/utils/adt/xid8funcs.c index d8e40b3b96..3af9ebadce 100644 --- a/src/backend/utils/adt/xid8funcs.c +++ b/src/backend/utils/adt/xid8funcs.c @@ -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); } /*