v2-0001-Fix-stale-relation-close-in-sequence-synchronization.patch

From 75672fedf247f045ee772cf365ff62e0c0bcacdb Mon Sep 17 00:00:00 2001
From: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Date: Tue, 28 Apr 2026 16:37:15 +0530
Subject: [PATCH v2] Fix stale relation close in sequence synchronization

copy_sequences() processes publisher sequence data one result row at a time,
but kept the Relation pointer used for the local sequence at batch scope. If
pg_get_sequence_data() returned NULL sequence data for a later row,
get_and_validate_seq_info() could return COPYSEQ_SKIPPED before assigning a
new relation to that output argument. The caller could then close the stale
Relation pointer left from the previous row, tripping the relcache refcount
assertion in assert-enabled builds.

This is not limited to concurrent drops. pg_get_sequence_data() also returns
NULL data when the publisher connection user cannot read the sequence.

Keep the caller-side Relation pointer local to each publisher result row and
initialize the output Relation in get_and_validate_seq_info(), so early return
paths cannot reuse a relation from a previous row. Add a subscription test
that syncs readable sequences followed by a published sequence for which the
replication user lacks SELECT.
---
 .../replication/logical/sequencesync.c        |  8 +++--
 src/test/subscription/t/036_sequences.pl      | 36 +++++++++++++++++++
 2 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/src/backend/replication/logical/sequencesync.c b/src/backend/replication/logical/sequencesync.c
index ec7e76abf93..adc0ebadac3 100644
--- a/src/backend/replication/logical/sequencesync.c
+++ b/src/backend/replication/logical/sequencesync.c
@@ -246,6 +246,8 @@ get_and_validate_seq_info(TupleTableSlot *slot, Relation *sequence_rel,
 	Form_pg_sequence local_seq;
 	LogicalRepSequenceInfo *seqinfo_local;
 
+	*sequence_rel = NULL;
+
 	*seqidx = DatumGetInt32(slot_getattr(slot, ++col, &isnull));
 	Assert(!isnull);
 
@@ -254,8 +256,8 @@ get_and_validate_seq_info(TupleTableSlot *slot, Relation *sequence_rel,
 		(LogicalRepSequenceInfo *) list_nth(seqinfos, *seqidx);
 
 	/*
-	 * last_value can be NULL if the sequence was dropped concurrently (see
-	 * pg_get_sequence_data()).
+	 * The sequence data can be NULL if it is not accessible on the publisher
+	 * (see pg_get_sequence_data()).
 	 */
 	datum = slot_getattr(slot, ++col, &isnull);
 	if (isnull)
@@ -411,7 +413,6 @@ copy_sequences(WalReceiverConn *conn)
 		int			batch_skipped_count = 0;
 		int			batch_insuffperm_count = 0;
 		int			batch_missing_count;
-		Relation	sequence_rel = NULL;
 
 		WalRcvExecResult *res;
 		TupleTableSlot *slot;
@@ -494,6 +495,7 @@ copy_sequences(WalReceiverConn *conn)
 		{
 			CopySeqResult sync_status;
 			LogicalRepSequenceInfo *seqinfo;
+			Relation	sequence_rel = NULL;
 			int			seqidx;
 
 			CHECK_FOR_INTERRUPTS();
diff --git a/src/test/subscription/t/036_sequences.pl b/src/test/subscription/t/036_sequences.pl
index 471780a3585..53233920edf 100644
--- a/src/test/subscription/t/036_sequences.pl
+++ b/src/test/subscription/t/036_sequences.pl
@@ -221,4 +221,40 @@ $node_subscriber->wait_for_log(
 	qr/WARNING: ( [A-Z0-9]+:)? missing sequence on publisher \("public.regress_s4"\)/,
 	$log_offset);
 
+##########
+# A NULL sequence data row from the publisher must not make the subscriber
+# close the previously synchronized sequence relation again.
+##########
+
+$node_publisher->safe_psql(
+	'postgres', qq(
+	CREATE ROLE regress_seq_repl LOGIN REPLICATION;
+	CREATE SEQUENCE regress_no_select;
+	SELECT nextval('regress_no_select');
+	GRANT USAGE ON SCHEMA public TO regress_seq_repl;
+	GRANT SELECT ON ALL SEQUENCES IN SCHEMA public TO regress_seq_repl;
+	REVOKE ALL ON SEQUENCE regress_no_select FROM PUBLIC;
+	REVOKE ALL ON SEQUENCE regress_no_select FROM regress_seq_repl;
+));
+
+$node_subscriber->safe_psql('postgres',
+	qq(CREATE SEQUENCE regress_no_select;));
+
+my $publisher_limited_connstr =
+  $node_publisher->connstr . ' dbname=postgres user=regress_seq_repl';
+$log_offset = -s $node_subscriber->logfile;
+
+$node_subscriber->safe_psql(
+	'postgres',
+	"CREATE SUBSCRIPTION regress_seq_sub_no_select CONNECTION '$publisher_limited_connstr' PUBLICATION regress_seq_pub WITH (disable_on_error = true)"
+);
+
+$node_subscriber->wait_for_log(
+	qr/WARNING: ( [A-Z0-9]+:)? missing sequence on publisher \("public.regress_no_select"\)/,
+	$log_offset);
+
+$result = $node_subscriber->safe_psql('postgres', 'SELECT 1');
+is($result, '1',
+	'subscriber remains running after publisher returns NULL sequence data');
+
 done_testing();
-- 
2.34.1