From 3f67523bac084964c0e780fddd509f3464d32282 Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Wed, 8 Mar 2023 11:37:05 -0800 Subject: [PATCH v5 1/8] 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. 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 4fcfd6df72d..33c5b338959 100644 --- a/contrib/amcheck/verify_heapam.c +++ b/contrib/amcheck/verify_heapam.c @@ -1576,6 +1576,9 @@ 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); @@ -1597,8 +1600,8 @@ 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); } /* -- 2.38.0