v1-0001-pg_rewind-warn-if-we-haven-t-checkpointed-after-p.patch

From 47ae21af8fd2d685987b10c3195e4897c1f81976 Mon Sep 17 00:00:00 2001
From: jcoleman <jtc331@gmail.com>
Date: Fri, 3 Jun 2022 20:32:15 -0400
Subject: [PATCH v1] pg_rewind: warn if we haven't checkpointed after promote

Because pg_rewind looks at the last checkpoint to determine the timeline
on the source server it can incorrectly report that the timelines are
the same if the source is a recently promoted standby that hasn't yet
completed a new checkpoint.

This is already documented, but we shouldn't tell the user a rewind
isn't necessary when it clearly is.
---
 src/bin/pg_rewind/pg_rewind.c                 | 13 +++-
 .../t/010_no_checkpoint_after_promotion.pl    | 74 +++++++++++++++++++
 src/bin/pg_rewind/t/RewindTest.pm             | 22 ++++--
 3 files changed, 101 insertions(+), 8 deletions(-)
 create mode 100644 src/bin/pg_rewind/t/010_no_checkpoint_after_promotion.pl

diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c
index 1ff8da1676..2dc396c4fd 100644
--- a/src/bin/pg_rewind/pg_rewind.c
+++ b/src/bin/pg_rewind/pg_rewind.c
@@ -337,8 +337,19 @@ main(int argc, char **argv)
 	 *
 	 * If both clusters are already on the same timeline, there's nothing to
 	 * do.
+	 *
+	 * We must avoid assuming that a checkpoint has happened on the source or
+	 * we'll possibly conclude the timelines are the same when the source has
+	 * recently promoted.
 	 */
-	if (ControlFile_target.checkPointCopy.ThisTimeLineID ==
+	if (ControlFile_source.minRecoveryPointTLI != 0 &&
+			ControlFile_source.checkPointCopy.ThisTimeLineID !=
+			ControlFile_source.minRecoveryPointTLI)
+	{
+		pg_log_info("source cluster hasn't checkpointed since its last timeline switch");
+		exit(1);
+	}
+	else if (ControlFile_target.checkPointCopy.ThisTimeLineID ==
 		ControlFile_source.checkPointCopy.ThisTimeLineID)
 	{
 		pg_log_info("source and target cluster are on the same timeline");
diff --git a/src/bin/pg_rewind/t/010_no_checkpoint_after_promotion.pl b/src/bin/pg_rewind/t/010_no_checkpoint_after_promotion.pl
new file mode 100644
index 0000000000..53188b2514
--- /dev/null
+++ b/src/bin/pg_rewind/t/010_no_checkpoint_after_promotion.pl
@@ -0,0 +1,74 @@
+
+# Copyright (c) 2021-2022, PostgreSQL Global Development Group
+
+use strict;
+use warnings;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+use FindBin;
+use lib $FindBin::RealBin;
+
+use RewindTest;
+
+RewindTest::setup_cluster("remote");
+RewindTest::start_primary();
+
+# Create a test table and insert a row in primary.
+primary_psql("CREATE TABLE tbl1 (d text)");
+primary_psql("INSERT INTO tbl1 VALUES ('in primary')");
+
+# This test table will be used to test truncation, i.e. the table
+# is extended in the old primary after promotion
+primary_psql("CREATE TABLE trunc_tbl (d text)");
+primary_psql("INSERT INTO trunc_tbl VALUES ('in primary')");
+
+# This test table will be used to test the "copy-tail" case, i.e. the
+# table is truncated in the old primary after promotion
+primary_psql("CREATE TABLE tail_tbl (id integer, d text)");
+primary_psql("INSERT INTO tail_tbl VALUES (0, 'in primary')");
+
+# This test table is dropped in the old primary after promotion.
+primary_psql("CREATE TABLE drop_tbl (d text)");
+primary_psql("INSERT INTO drop_tbl VALUES ('in primary')");
+
+primary_psql("CHECKPOINT");
+
+RewindTest::create_standby("remote");
+
+# Insert additional data on primary that will be replicated to standby
+primary_psql("INSERT INTO tbl1 values ('in primary, before promotion')");
+primary_psql(
+  "INSERT INTO trunc_tbl values ('in primary, before promotion')");
+primary_psql(
+  "INSERT INTO tail_tbl SELECT g, 'in primary, before promotion: ' || g FROM generate_series(1, 10000) g"
+);
+
+primary_psql('CHECKPOINT');
+
+RewindTest::promote_standby('skip_checkpoint' => 1);
+
+# Insert a row in the old primary. This causes the primary and standby
+# to have "diverged", it's no longer possible to just apply the
+# standy's logs over primary directory - you need to rewind.
+primary_psql("INSERT INTO tbl1 VALUES ('in primary, after promotion')");
+
+# Also insert a new row in the standby, which won't be present in the
+# old primary.
+standby_psql("INSERT INTO tbl1 VALUES ('in standby, after promotion')");
+
+$node_primary->stop;
+
+my $primary_pgdata = $node_primary->data_dir;
+my $standby_connstr = $node_standby->connstr('postgres');
+command_fails_like(
+  [
+    'pg_rewind',       '--dry-run',
+    "--source-server", $standby_connstr,
+    '--target-pgdata', $primary_pgdata,
+    '--no-sync',       '--no-ensure-shutdown'
+  ],
+  qr/source cluster hasn\'t checkpointed since its last timeline switch/,
+  'pg_rewind no checkpoint after promotion');
+
+done_testing();
diff --git a/src/bin/pg_rewind/t/RewindTest.pm b/src/bin/pg_rewind/t/RewindTest.pm
index 98b66b01f8..89fddc1656 100644
--- a/src/bin/pg_rewind/t/RewindTest.pm
+++ b/src/bin/pg_rewind/t/RewindTest.pm
@@ -188,6 +188,11 @@ primary_conninfo='$connstr_primary'
 
 sub promote_standby
 {
+	my (%options) = (
+		'skip_checkpoint' => 0,
+		@_
+	);
+
 	#### Now run the test-specific parts to run after standby has been started
 	# up standby
 
@@ -198,13 +203,16 @@ sub promote_standby
 	# the primary out-of-sync with the standby.
 	$node_standby->promote;
 
-	# Force a checkpoint after the promotion. pg_rewind looks at the control
-	# file to determine what timeline the server is on, and that isn't updated
-	# immediately at promotion, but only at the next checkpoint. When running
-	# pg_rewind in remote mode, it's possible that we complete the test steps
-	# after promotion so quickly that when pg_rewind runs, the standby has not
-	# performed a checkpoint after promotion yet.
-	standby_psql("checkpoint");
+	unless ($options{'skip_checkpoint'})
+	{
+		# Force a checkpoint after the promotion. pg_rewind looks at the control
+		# file to determine what timeline the server is on, and that isn't updated
+		# immediately at promotion, but only at the next checkpoint. When running
+		# pg_rewind in remote mode, it's possible that we complete the test steps
+		# after promotion so quickly that when pg_rewind runs, the standby has not
+		# performed a checkpoint after promotion yet.
+		standby_psql("checkpoint");
+	}
 
 	return;
 }
-- 
2.32.0 (Apple Git-132)