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amcheck: Fix ordering bug in update_cached_xid_range()

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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
This commit is contained in:
Andres Freund 2023-03-11 14:12:51 -08:00
parent 4e633016ab
commit 16327240da
1 changed files with 4 additions and 1 deletions
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5
contrib/amcheck/verify_heapam.c
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@ -1576,6 +1576,9 @@ FullTransactionIdFromXidAndCtx(TransactionId xid, const HeapCheckContext *ctx)
{ {
uint32 epoch; uint32 epoch;
Assert(TransactionIdIsNormal(ctx->next_xid));
Assert(FullTransactionIdIsNormal(ctx->next_fxid));
if (!TransactionIdIsNormal(xid)) if (!TransactionIdIsNormal(xid))
return FullTransactionIdFromEpochAndXid(0, xid); return FullTransactionIdFromEpochAndXid(0, xid);
epoch = EpochFromFullTransactionId(ctx->next_fxid); epoch = EpochFromFullTransactionId(ctx->next_fxid);
@ -1597,8 +1600,8 @@ update_cached_xid_range(HeapCheckContext *ctx)
LWLockRelease(XidGenLock); LWLockRelease(XidGenLock);
/* And compute alternate versions of the same */ /* And compute alternate versions of the same */
ctx->oldest_fxid = FullTransactionIdFromXidAndCtx(ctx->oldest_xid, ctx);
ctx->next_xid = XidFromFullTransactionId(ctx->next_fxid); ctx->next_xid = XidFromFullTransactionId(ctx->next_fxid);
ctx->oldest_fxid = FullTransactionIdFromXidAndCtx(ctx->oldest_xid, ctx);
} }
/* /*