Backpatch tuplesort.c assertion.

Backpatch an assertion (that was originally added to Postgres 12 by
commit dd299df8189) that seems broadly useful.  The assertion can detect
violations of the HOT invariant (i.e. no two index tuples can point to
the same heap TID) when CREATE INDEX somehow incorrectly allows that to
take place.

For example, a IndexBuildHeapScan/heapam_index_build_range_scan bug
might result in two tuples that both point to the same heap TID.  If
these two tuples also happen to be duplicates, the assertion will fail.

Discussion: https://postgr.es/m/CAH2-WzmBxu4o=pMsniur+bwHqCGCmV_AOLkuK6BuU7ngA6evqw@mail.gmail.com
Backpatch: 9.5-11 only

diff --git a/src/backend/utils/sort/tuplesort.c b/src/backend/utils/sort/tuplesort.c
index f895a3ae743d52bf4a02ab42e87e04e7e95a8855..d49f024e43151041f12f6efbd2dce3d6d25ff747 100644 (file)
--- a/src/backend/utils/sort/tuplesort.c
+++ b/src/backend/utils/sort/tuplesort.c
@@ -4173,6 +4173,9 @@ comparetup_index_btree(const SortTuple *a, const SortTuple *b,
            return (pos1 < pos2) ? -1 : 1;
    }
 
+   /* ItemPointer values should never be equal */
+   Assert(false);
+
    return 0;
 }
 
@@ -4225,6 +4228,9 @@ comparetup_index_hash(const SortTuple *a, const SortTuple *b,
            return (pos1 < pos2) ? -1 : 1;
    }
 
+   /* ItemPointer values should never be equal */
+   Assert(false);
+
    return 0;
 }