Backpatch tuplesort.c assertion.

petergeoghegan · petergeoghegan · commit b6608ae5d3cc · 2020-07-29T16:00:48.000-07:00
Backpatch an assertion (that was originally added to Postgres 12 by commit dd299df) 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
@@ -3682,6 +3682,9 @@ comparetup_index_btree(const SortTuple *a, const SortTuple *b,
 			return (pos1 < pos2) ? -1 : 1;
 	}
 
+	/* ItemPointer values should never be equal */
+	Assert(false);
+
 	return 0;
 }
 
@@ -3731,6 +3734,9 @@ comparetup_index_hash(const SortTuple *a, const SortTuple *b,
 			return (pos1 < pos2) ? -1 : 1;
 	}
 
+	/* ItemPointer values should never be equal */
+	Assert(false);
+
 	return 0;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -3682,6 +3682,9 @@ comparetup_index_btree(const SortTuple a, const SortTuple b,`
`3682`	`3682`	`return (pos1 < pos2) ? -1 : 1;`
`3683`	`3683`	`}`
`3684`	`3684`
	`3685`	`+ /* ItemPointer values should never be equal */`
	`3686`	`+ Assert(false);`
	`3687`	`+`
`3685`	`3688`	`return 0;`
`3686`	`3689`	`}`
`3687`	`3690`
`@@ -3731,6 +3734,9 @@ comparetup_index_hash(const SortTuple a, const SortTuple b,`
`3731`	`3734`	`return (pos1 < pos2) ? -1 : 1;`
`3732`	`3735`	`}`
`3733`	`3736`
	`3737`	`+ /* ItemPointer values should never be equal */`
	`3738`	`+ Assert(false);`
	`3739`	`+`
`3734`	`3740`	`return 0;`
`3735`	`3741`	`}`
`3736`	`3742`