Demote pg_unreachable() in heapam to an assertion.

petergeoghegan · petergeoghegan · commit bd9f4cf0ee53 · 2021-10-29T10:53:46.000-07:00
Commit d168b66, which overhauled index deletion, added a pg_unreachable() to the end of a sort comparator used when sorting heap TIDs from an index page. This allows the compiler to apply optimizations that assume that the heap TIDs from the index AM must always be unique. That doesn't seem like a good idea now, given recent reports of corruption involving duplicate TIDs in indexes on Postgres 14. Demote to an assertion, just in case. Backpatch: 14-, where index deletion was overhauled.
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
@@ -7579,7 +7579,7 @@ index_delete_sort_cmp(TM_IndexDelete *deltid1, TM_IndexDelete *deltid2)
 			return (pos1 < pos2) ? -1 : 1;
 	}
 
-	pg_unreachable();
+	Assert(false);
 
 	return 0;
 }

Original file line number	Diff line number	Diff line change
`@@ -7579,7 +7579,7 @@ index_delete_sort_cmp(TM_IndexDelete deltid1, TM_IndexDelete deltid2)`
`7579`	`7579`	`return (pos1 < pos2) ? -1 : 1;`
`7580`	`7580`	`}`
`7581`	`7581`
`7582`		`- pg_unreachable();`
	`7582`	`+ Assert(false);`
`7583`	`7583`
`7584`	`7584`	`return 0;`
`7585`	`7585`	`}`