amcheck: Fix verify_heapam for tuples where xmin or xmax is 0.

robertmhaas · robertmhaas · commit 8fd5aa76c367 · 2023-03-24T11:06:45.000-04:00
In such cases, get_xid_status() doesn't set its output parameter (the third argument), so we shouldn't fall through to code which will test the value of that parameter. There are five existing calls to get_xid_status(), three of which seem to already handle this case properly. This commit tries to fix the other two. If we're checking xmin and find that it is invalid (i.e. 0) just report that as corruption, similar to what's already done in the three cases that seem correct. If we're checking xmax and find that's invalid, that's fine: it just means that the tuple hasn't been updated or deleted. Thanks to Andres Freund and valgrind for finding this problem, and also to Andres for having a look at the patch. This bug seems to go all the way back to where verify_heapam was first introduced, but wasn't detected until recently, possibly because of the new test cases added for update chain verification. Back-patch to v14, where this code showed up. Discussion: http://postgr.es/m/CA+TgmoZAYzQZqyUparXy_ks3OEOfLD9-bEXt8N-2tS1qghX9gQ@mail.gmail.com
diff --git a/contrib/amcheck/verify_heapam.c b/contrib/amcheck/verify_heapam.c
@@ -774,6 +774,9 @@ check_tuple_visibility(HeapCheckContext *ctx)
 	switch (get_xid_status(xmin, ctx, &xmin_status))
 	{
 		case XID_INVALID:
+			report_corruption(ctx,
+							  pstrdup("xmin is invalid"));
+			return false;
 		case XID_BOUNDS_OK:
 			break;
 		case XID_IN_FUTURE:
@@ -1109,6 +1112,9 @@ check_tuple_visibility(HeapCheckContext *ctx)
 	xmax = HeapTupleHeaderGetRawXmax(tuphdr);
 	switch (get_xid_status(xmax, ctx, &xmax_status))
 	{
+		case XID_INVALID:
+			ctx->tuple_could_be_pruned = false;
+			return true;
 		case XID_IN_FUTURE:
 			report_corruption(ctx,
 							  psprintf("xmax %u equals or exceeds next valid transaction ID %u:%u",
@@ -1131,7 +1137,6 @@ check_tuple_visibility(HeapCheckContext *ctx)
 									   XidFromFullTransactionId(ctx->oldest_fxid)));
 			return false;		/* corrupt */
 		case XID_BOUNDS_OK:
-		case XID_INVALID:
 			break;
 	}
 
