From 87732112c48550c848a6d6b18bae57f5e616ce2d Mon Sep 17 00:00:00 2001
From: Masahiko Sawada <sawada.mshk@gmail.com>
Date: Mon, 9 Nov 2026 11:52:02 -0800
Subject: [PATCH] Add test for slot sync persisting a slot without a consistent
 snapshot.

---
 src/test/recovery/meson.build                 |  1 +
 .../t/061_slotsync_persist_inconsistent.pl    | 96 +++++++++++++++++++
 2 files changed, 97 insertions(+)
 create mode 100644 src/test/recovery/t/061_slotsync_persist_inconsistent.pl

diff --git a/src/test/recovery/meson.build b/src/test/recovery/meson.build
index 87dbdb6326e..dbd776cbd80 100644
--- a/src/test/recovery/meson.build
+++ b/src/test/recovery/meson.build
@@ -68,6 +68,7 @@ tests += {
       't/057_snapshot_commit_race.pl',
       't/059_remote_apply_status_interval.pl',
       't/060_multixact_crashed_updater.pl',
+      't/061_slotsync_persist_inconsistent.pl',
     ],
   },
 }
diff --git a/src/test/recovery/t/061_slotsync_persist_inconsistent.pl b/src/test/recovery/t/061_slotsync_persist_inconsistent.pl
new file mode 100644
index 00000000000..98f3df35634
--- /dev/null
+++ b/src/test/recovery/t/061_slotsync_persist_inconsistent.pl
@@ -0,0 +1,96 @@
+
+# Copyright (c) 2026, PostgreSQL Global Development Group
+
+# Slot synchronization must keep a synced slot temporary until the standby
+# can build a consistent snapshot from its restart_lsn.  Since commit
+# 788ec96d591, update_and_persist_local_synced_slot() decides from
+# slotsync_skip_reason, which a no-op sync cycle resets to SS_SKIP_NONE,
+# so a slot that failed the consistency check in one cycle is persisted in
+# the next one.  Once the primary slot advances, the next sync of that
+# now-persistent slot hits Assert(persistency == RS_TEMPORARY) at
+# slotsync.c:364.
+
+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 => 'logical');
+$primary->append_conf('postgresql.conf', "autovacuum = off");
+$primary->start;
+$primary->safe_psql(
+	'postgres', q{
+	CREATE TABLE t (a int);
+	SELECT pg_create_physical_replication_slot('phys');
+	SELECT pg_create_logical_replication_slot('fslot', 'test_decoding',
+											  false, false, true);
+});
+
+$primary->backup('bkp');
+my $connstr = $primary->connstr;
+my $standby = PostgreSQL::Test::Cluster->new('standby');
+$standby->init_from_backup($primary, 'bkp', has_streaming => 1);
+$standby->append_conf(
+	'postgresql.conf', qq{
+hot_standby_feedback = on
+primary_slot_name = 'phys'
+primary_conninfo = '$connstr dbname=postgres'
+});
+$standby->start;
+$primary->wait_for_replay_catchup($standby);
+
+# Pause replay so that the standby never sees the xid assigned below;
+# the synced slot's catalog_xmin then equals the primary slot's.
+$standby->safe_psql('postgres', 'SELECT pg_wal_replay_pause()');
+
+# An open transaction with an xid, and a running_xacts record listing it.
+my $xact = $primary->background_psql('postgres');
+my $xid = $xact->query_safe('BEGIN; SELECT pg_current_xact_id()');
+
+# Each statement in its own transaction; the second get_changes moves the
+# slot's restart_lsn to the running_xacts record above.
+$primary->safe_psql('postgres', 'SELECT pg_log_standby_snapshot()');
+$primary->safe_psql('postgres', 'INSERT INTO t VALUES (1)');
+$primary->safe_psql('postgres',
+	"SELECT pg_logical_slot_get_changes('fslot', NULL, NULL)") for 1 .. 2;
+
+my ($catalog_xmin, $confirmed_flush) = split /\|/,
+  $primary->safe_psql('postgres',
+	"SELECT catalog_xmin, confirmed_flush_lsn FROM pg_replication_slots WHERE slot_name = 'fslot'"
+  );
+is($catalog_xmin, $xid, 'primary slot restart point lists the open xid');
+
+$standby->poll_query_until('postgres',
+	"SELECT pg_last_wal_receive_lsn() >= '$confirmed_flush'::pg_lsn");
+
+# Synchronize.  The call blocks in SnapBuildWaitSnapshot() until the open
+# transaction ends, then fails to reach a consistent point before the
+# confirmed_flush_lsn and retries 200ms later.
+my $log_offset = -s $standby->logfile;
+my $sync = $standby->background_psql('postgres', on_error_stop => 0);
+$sync->query_until(
+	qr/start/, q{
+	\echo start
+	SELECT pg_sync_replication_slots();
+});
+$standby->safe_psql('postgres', 'SELECT pg_wal_replay_resume()');
+$standby->wait_for_log(qr/Waiting for transactions/, $log_offset);
+$xact->quit;
+
+$standby->wait_for_log(qr/could not synchronize replication slot "fslot"/,
+	$log_offset);
+$standby->wait_for_log(
+	qr/newly created replication slot "fslot" is sync-ready now/,
+	$log_offset);
+$sync->quit;
+
+is( $standby->safe_psql(
+		'postgres',
+		"SELECT temporary FROM pg_replication_slots WHERE slot_name = 'fslot'"
+	),
+	't',
+	'synced slot without a consistent snapshot stays temporary');
+
+done_testing();
-- 
2.56.0