postgres.git / summary / log / commit / refs

commit    a42f515d6b45ea19b96fb2868d8acb77251d911d
Author:   Andres Freund <andres@anarazel.de>
Date:     Sat Mar 11 22:12:51 2023 +0000
First released in: 16.0, 14.8, 15.3

    amcheck: Fix ordering bug in update_cached_xid_range()
    
    The initialization order in update_cached_xid_range() was wrong, calling
    FullTransactionIdFromXidAndCtx() before setting
    ->next_xid. FullTransactionIdFromXidAndCtx() uses ->next_xid.
    
    In most situations this will not cause visible issues, because the next call
    to update_cached_xid_range() will use a less wrong ->next_xid. It's rare that
    xids advance fast enough for this to be a problem.
    
    Found while adding more asserts to the 64bit xid infrastructure.
    
    Reviewed-by: Mark Dilger <mark.dilger@enterprisedb.com>
    Discussion: https://postgr.es/m/20230108002923.cyoser3ttmt63bfn@awork3.anarazel.de
    Backpatch: 14-, where heapam verification was introduced


 contrib/amcheck/verify_heapam.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/contrib/amcheck/verify_heapam.c b/contrib/amcheck/verify_heapam.c
index 30064d0aba9..b237ee9156c 100644
--- a/contrib/amcheck/verify_heapam.c
+++ b/contrib/amcheck/verify_heapam.c
@@ -1578,6 +1578,9 @@ FullTransactionIdFromXidAndCtx(TransactionId xid, const HeapCheckContext *ctx)
 {
 	uint32		epoch;
 
+	Assert(TransactionIdIsNormal(ctx->next_xid));
+	Assert(FullTransactionIdIsNormal(ctx->next_fxid));
+
 	if (!TransactionIdIsNormal(xid))
 		return FullTransactionIdFromEpochAndXid(0, xid);
 	epoch = EpochFromFullTransactionId(ctx->next_fxid);
@@ -1599,8 +1602,8 @@ update_cached_xid_range(HeapCheckContext *ctx)
 	LWLockRelease(XidGenLock);
 
 	/* And compute alternate versions of the same */
-	ctx->oldest_fxid = FullTransactionIdFromXidAndCtx(ctx->oldest_xid, ctx);
 	ctx->next_xid = XidFromFullTransactionId(ctx->next_fxid);
+	ctx->oldest_fxid = FullTransactionIdFromXidAndCtx(ctx->oldest_xid, ctx);
 }
 
 /*


[parent: 786528039911]