From 87dd4f2e14c198c5130fab13eb3e36516d4df58c Mon Sep 17 00:00:00 2001
From: shihao zhong <zhong950419@gmail.com>
Date: Sat, 24 Oct 2026 01:00:36 -0400
Subject: [PATCH] Add test for incremental backup after promotion at a recovery
 target

A standby can summarize WAL past its recovery target. If that WAL
truncates a table, the next incremental backup on the promoted server
skips blocks changed before the target, and the restored copy has old
data.
---
 src/bin/pg_combinebackup/meson.build          |  1 +
 .../t/014_truncation_after_target.pl          | 82 +++++++++++++++++++
 2 files changed, 83 insertions(+)
 create mode 100644 src/bin/pg_combinebackup/t/014_truncation_after_target.pl

diff --git a/src/bin/pg_combinebackup/meson.build b/src/bin/pg_combinebackup/meson.build
index ba1c8cfa3d0..369619bce64 100644
--- a/src/bin/pg_combinebackup/meson.build
+++ b/src/bin/pg_combinebackup/meson.build
@@ -40,6 +40,7 @@ tests += {
       't/010_hardlink.pl',
       't/011_ib_truncation.pl',
       't/012_vm_consistency.pl',
+      't/014_truncation_after_target.pl',
     ],
   }
 }
diff --git a/src/bin/pg_combinebackup/t/014_truncation_after_target.pl b/src/bin/pg_combinebackup/t/014_truncation_after_target.pl
new file mode 100644
index 00000000000..c30a7e88199
--- /dev/null
+++ b/src/bin/pg_combinebackup/t/014_truncation_after_target.pl
@@ -0,0 +1,82 @@
+# Copyright (c) 2026, PostgreSQL Global Development Group
+#
+# A standby can summarize WAL past its recovery target.  If that WAL
+# truncates a table, an incremental backup taken after promotion must still
+# include blocks modified before the target.
+
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+my $primary = PostgreSQL::Test::Cluster->new('primary');
+$primary->init(allows_streaming => 1);
+$primary->append_conf('postgresql.conf', <<EOF);
+summarize_wal = on
+autovacuum = off
+EOF
+$primary->start;
+
+# One row per block.
+my $pad_size = $primary->safe_psql('postgres', 'SHOW block_size') / 2;
+$primary->safe_psql('postgres', <<EOF);
+CREATE TABLE t (id int, v int, pad text STORAGE PLAIN);
+INSERT INTO t SELECT g, 0, repeat('x', $pad_size) FROM generate_series(1, 4) g;
+VACUUM t;
+EOF
+
+$primary->backup('full');
+my $full_path = $primary->backup_dir . '/full';
+
+my $standby = PostgreSQL::Test::Cluster->new('standby');
+$standby->init_from_backup($primary, 'full', has_streaming => 1);
+$standby->append_conf('postgresql.conf', <<EOF);
+summarize_wal = on
+recovery_target_action = 'pause'
+EOF
+
+# Modify the last block, and stop recovery right after that.
+$primary->safe_psql('postgres', 'UPDATE t SET v = 1 WHERE id = 4');
+my $target =
+  $primary->safe_psql('postgres', 'SELECT pg_current_wal_insert_lsn()');
+$standby->append_conf('postgresql.conf', "recovery_target_lsn = '$target'\n");
+$standby->start;
+
+# Truncate the table on the old timeline only.
+$primary->safe_psql('postgres', 'DELETE FROM t WHERE id > 1');
+$primary->safe_psql('postgres', 'VACUUM t');
+$primary->safe_psql('postgres', 'SELECT pg_switch_wal()');
+$primary->safe_psql('postgres', 'CHECKPOINT');
+
+$standby->poll_query_until('postgres',
+	"SELECT pg_get_wal_replay_pause_state() = 'paused'")
+  or die "standby did not pause at the target";
+
+# Give the summarizer time to get past the target, if it is going to.
+sleep(5);
+
+$primary->stop;
+$standby->safe_psql('postgres', 'SELECT pg_promote()');
+$standby->poll_query_until('postgres', 'SELECT NOT pg_is_in_recovery()')
+  or die "standby was not promoted";
+
+# Back up before reading t, so that setting hint bits can't hide the problem.
+$standby->command_ok(
+	[
+		'pg_basebackup', '--no-sync',
+		'--pgdata' => $primary->backup_dir . '/incr',
+		'--checkpoint' => 'fast',
+		'--incremental' => "$full_path/backup_manifest",
+	],
+	'incremental backup after promotion');
+$standby->stop;
+
+my $restored = PostgreSQL::Test::Cluster->new('restored');
+$restored->init_from_backup($primary, 'incr', combine_with_prior => ['full']);
+$restored->start;
+is($restored->safe_psql('postgres', 'SELECT id, v FROM t ORDER BY id'),
+	"1|0\n2|0\n3|0\n4|1", 'restored backup has the update');
+$restored->stop;
+
+done_testing();