From c87aff065c33e1a3c9bf0350f9160e84bfce1c36 Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Mon, 27 Mar 2023 13:37:16 -0400
Subject: [PATCH] amcheck: Generalize one of the recently-added update chain
 checks.

Commit bbc1376b39627c6bddd8a0dc0a7dda24c91a97a0 checked that if
a redirected line pointer pointed to a tuple, the tuple should be
marked both HEAP_ONLY_TUPLE and HEAP_UPDATED. But Andres Freund
pointed out that *any* tuple that is marked HEAP_ONLY_TUPLE should
be marked HEAP_UPDATED, not just one that is the target of a
redirected line pointer. Do that instead.

To see why this is better, consider a redirect line pointer A
which points to a heap-only tuple B which points (via CTID)
to another heap-only tuple C. With the old code, we'd complain
if B was not marked HEAP_UPDATED, but with this change, we'll
complain if either B or C is not marked HEAP_UPDATED.

(Note that, with or without this commit, if either B or C were
not marked HEAP_ONLY_TUPLE, we would also complain about that.)

Discussion: http://postgr.es/m/CA%2BTgmobLypZx%3DcOH%2ByY1GZmCruaoucHm77A6y_-Bo%3Dh-_3H28g%40mail.gmail.com
---
 contrib/amcheck/verify_heapam.c           | 20 +++++++++-----------
 src/bin/pg_amcheck/t/004_verify_heapam.pl | 11 +++++------
 2 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/contrib/amcheck/verify_heapam.c b/contrib/amcheck/verify_heapam.c
index 1dc9d89f30..ce3114f4e6 100644
--- a/contrib/amcheck/verify_heapam.c
+++ b/contrib/amcheck/verify_heapam.c
@@ -624,17 +624,6 @@ verify_heapam(PG_FUNCTION_ARGS)
 											   (unsigned) nextoffnum));
 				}
 
-				/*
-				 * Redirects are created by updates, so successor should be
-				 * the result of an update.
-				 */
-				if ((next_htup->t_infomask & HEAP_UPDATED) == 0)
-				{
-					report_corruption(&ctx,
-									  psprintf("redirected line pointer points to a non-heap-updated tuple at offset %u",
-											   (unsigned) nextoffnum));
-				}
-
 				/* HOT chains should not intersect. */
 				if (predecessor[nextoffnum] != InvalidOffsetNumber)
 				{
@@ -954,6 +943,15 @@ check_tuple_header(HeapCheckContext *ctx)
 		 */
 	}
 
+	if (HeapTupleHeaderIsHeapOnly(tuphdr) &&
+		((tuphdr->t_infomask & HEAP_UPDATED) == 0))
+	{
+		report_corruption(ctx,
+						  psprintf("tuple is heap only, but not the result of an update"));
+
+		/* Here again, we can still perform further checks. */
+	}
+
 	if (infomask & HEAP_HASNULL)
 		expected_hoff = MAXALIGN(SizeofHeapTupleHeader + BITMAPLEN(ctx->natts));
 	else
diff --git a/src/bin/pg_amcheck/t/004_verify_heapam.pl b/src/bin/pg_amcheck/t/004_verify_heapam.pl
index cc4aa4af87..90ba59ec0b 100644
--- a/src/bin/pg_amcheck/t/004_verify_heapam.pl
+++ b/src/bin/pg_amcheck/t/004_verify_heapam.pl
@@ -617,12 +617,10 @@ for (my $tupidx = 0; $tupidx < $ROWCOUNT; $tupidx++)
 	}
 	elsif ($offnum == 17)
 	{
-		# at offnum 19 we will unset HEAP_ONLY_TUPLE and HEAP_UPDATED flags.
+		# at offnum 19 we will unset HEAP_ONLY_TUPLE flag
 		die "offnum $offnum should be a redirect" if defined $tup;
 		push @expected,
 			qr/${header}redirected line pointer points to a non-heap-only tuple at offset \d+/;
-		push @expected,
-			qr/${header}redirected line pointer points to a non-heap-updated tuple at offset \d+/;
 	}
 	elsif ($offnum == 18)
 	{
@@ -637,10 +635,9 @@ for (my $tupidx = 0; $tupidx < $ROWCOUNT; $tupidx++)
 	}
 	elsif ($offnum == 19)
 	{
-		# unset HEAP_ONLY_TUPLE and HEAP_UPDATED flag, so that update chain
-		# validation will complain about offset 17
+		# unset HEAP_ONLY_TUPLE flag, so that update chain validation will
+		# complain about offset 17
 		$tup->{t_infomask2} &= ~HEAP_ONLY_TUPLE;
-		$tup->{t_infomask} &= ~HEAP_UPDATED;
 	}
 	elsif ($offnum == 22)
 	{
@@ -688,6 +685,8 @@ for (my $tupidx = 0; $tupidx < $ROWCOUNT; $tupidx++)
 		$tup->{t_infomask2} |= HEAP_ONLY_TUPLE;
 		push @expected,
 		  qr/${header}tuple is root of chain but is marked as heap-only tuple/;
+		push @expected,
+		  qr/${header}tuple is heap only, but not the result of an update/;
 	}
 	elsif ($offnum == 33)
 	{