v3-0001-Fix-missing-continuation-record-after-standby-pro.patch

From 17fbdb43c2d98ad4f3946f37a4d9f95ab38a2d2e Mon Sep 17 00:00:00 2001
From: "Sami Imseih (AWS)" <simseih@amazon.com>
Date: Fri, 25 Feb 2022 04:17:17 +0000
Subject: [PATCH 1/1] [PATCH v3] Fix "missing continuation record" after
 standby promotion

Fix a condition where a recently promoted standby attempts to write an
OVERWRITE_RECORD with an LSN of the previously read aborted record.

Author: Sami Imseih <simseih@amazon.com>
Discussion: https://postgr.es/m/44D259DE-7542-49C4-8A52-2AB01534DCA9@amazon.com
---
 src/backend/access/transam/xlog.c             |  15 ++-
 .../t/029_overwrite_contrecord_promotion.pl   | 111 ++++++++++++++++++
 2 files changed, 125 insertions(+), 1 deletion(-)
 create mode 100644 src/test/recovery/t/029_overwrite_contrecord_promotion.pl

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 0d2bd7a357..ae4dcba8df 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5427,7 +5427,17 @@ StartupXLOG(void)
 	if (!XLogRecPtrIsInvalid(missingContrecPtr))
 	{
 		Assert(!XLogRecPtrIsInvalid(abortedRecPtr));
-		EndOfLog = missingContrecPtr;
+		if (endOfRecoveryInfo->lastRec < missingContrecPtr)
+		{
+			elog(DEBUG2, "setting end of wal to missing continuation record %X/%X",
+				 LSN_FORMAT_ARGS(missingContrecPtr));
+			EndOfLog = missingContrecPtr;
+		}
+		else
+		{
+			elog(DEBUG2, "resetting aborted record");
+			abortedRecPtr = InvalidXLogRecPtr;
+		}
 	}
 
 	/*
@@ -6793,6 +6803,9 @@ CreateOverwriteContrecordRecord(XLogRecPtr aborted_lsn, XLogRecPtr pagePtr,
 
 	XLogFlush(recptr);
 
+	elog(DEBUG2, "OVERWRITE_CONTRECORD inserted at %X/%X for aborted record %X/%X",
+		 LSN_FORMAT_ARGS(ProcLastRecPtr), LSN_FORMAT_ARGS(xlrec.overwritten_lsn));
+
 	END_CRIT_SECTION();
 
 	return recptr;
diff --git a/src/test/recovery/t/029_overwrite_contrecord_promotion.pl b/src/test/recovery/t/029_overwrite_contrecord_promotion.pl
new file mode 100644
index 0000000000..e3511e89c1
--- /dev/null
+++ b/src/test/recovery/t/029_overwrite_contrecord_promotion.pl
@@ -0,0 +1,111 @@
+# Copyright (c) 2021-2022, PostgreSQL Global Development Group
+
+# Tests for resetting the "aborted record" after a promotion.
+
+use strict;
+use warnings;
+
+use FindBin;
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Test: Create a physical replica that's missing the last WAL file,
+# then restart the primary to create a divergent WAL file and observe
+# that the replica resets the "aborted record" after a promotion.
+
+my $node = PostgreSQL::Test::Cluster->new('primary');
+$node->init(allows_streaming => 1);
+# We need these settings for stability of WAL behavior.
+$node->append_conf(
+	'postgresql.conf', qq(
+autovacuum = off
+wal_keep_size = 1GB
+log_min_messages = DEBUG2
+));
+$node->start;
+
+$node->safe_psql('postgres', 'create table filler (a int, b text)');
+
+# Now consume all remaining room in the current WAL segment, leaving
+# space enough only for the start of a largish record.
+$node->safe_psql(
+	'postgres', q{
+DO $$
+DECLARE
+    wal_segsize int := setting::int FROM pg_settings WHERE name = 'wal_segment_size';
+    remain int;
+    iters  int := 0;
+BEGIN
+    LOOP
+        INSERT into filler
+        select g, repeat(md5(g::text), (random() * 60 + 1)::int)
+        from generate_series(1, 10) g;
+
+        remain := wal_segsize - (pg_current_wal_insert_lsn() - '0/0') % wal_segsize;
+        IF remain < 2 * setting::int from pg_settings where name = 'block_size' THEN
+            RAISE log 'exiting after % iterations, % bytes to end of WAL segment', iters, remain;
+            EXIT;
+        END IF;
+        iters := iters + 1;
+    END LOOP;
+END
+$$;
+});
+
+my $initfile = $node->safe_psql('postgres',
+	'SELECT pg_walfile_name(pg_current_wal_insert_lsn())');
+$node->safe_psql('postgres',
+	qq{SELECT pg_logical_emit_message(true, 'test 026', repeat('xyzxz', 123456))}
+);
+#$node->safe_psql('postgres', qq{create table foo ()});
+my$endfile = $node->safe_psql('postgres',
+	'SELECT pg_walfile_name(pg_current_wal_insert_lsn())');
+ok($initfile ne $endfile, "$initfile differs from $endfile");
+
+# Now stop abruptly, to avoid a stop checkpoint.  We can remove the tail file
+# afterwards, and on startup the large message should be overwritten with new
+# contents
+$node->stop('immediate');
+
+unlink $node->basedir . "/pgdata/pg_wal/$endfile"
+  or die "could not unlink " . $node->basedir . "/pgdata/pg_wal/$endfile: $!";
+
+# OK, create a standby at this spot.
+$node->backup_fs_cold('backup');
+my $node_standby = PostgreSQL::Test::Cluster->new('standby');
+$node_standby->init_from_backup($node, 'backup', has_streaming => 1);
+
+$node_standby->start;
+$node->start;
+
+$node->safe_psql('postgres',
+	qq{create table foo (a text); insert into foo values ('hello')});
+$node->safe_psql('postgres',
+	qq{SELECT pg_logical_emit_message(true, 'test 026', 'AABBCC')});
+
+my $until_lsn = $node->safe_psql('postgres', "SELECT pg_current_wal_lsn()");
+my $caughtup_query =
+  "SELECT '$until_lsn'::pg_lsn <= pg_last_wal_replay_lsn()";
+$node_standby->poll_query_until('postgres', $caughtup_query)
+  or die "Timed out while waiting for standby to catch up";
+
+ok($node_standby->safe_psql('postgres', 'select * from foo') eq 'hello',
+	'standby replays past overwritten contrecord');
+
+$ENV{PGDATA} = $node_standby->data_dir;
+$ENV{PGPORT} = $node_standby->port;
+$ENV{PGGHOST} = $node_standby->host;
+system "psql -c 'select pg_promote()'";
+
+# Verify message appears in standby's log
+my $log = slurp_file($node_standby->logfile);
+like(
+    $log,
+    qr[resetting aborted record],
+    "found log line in standby");
+
+$node->stop;
+$node_standby->stop;
+
+done_testing();
-- 
2.32.0