3 files changed, 116 insertions, 1 deletions
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 62f69ac20b2..47478969135 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -2157,9 +2157,10 @@ pg_stat_subscription_stats| SELECT ss.subid,
     ss.confl_update_missing,
     ss.confl_delete_origin_differs,
     ss.confl_delete_missing,
+    ss.confl_multiple_unique_conflicts,
     ss.stats_reset
    FROM pg_subscription s,
-    LATERAL pg_stat_get_subscription_stats(s.oid) ss(subid, apply_error_count, sync_error_count, confl_insert_exists, confl_update_origin_differs, confl_update_exists, confl_update_missing, confl_delete_origin_differs, confl_delete_missing, stats_reset);
+    LATERAL pg_stat_get_subscription_stats(s.oid) ss(subid, apply_error_count, sync_error_count, confl_insert_exists, confl_update_origin_differs, confl_update_exists, confl_update_missing, confl_delete_origin_differs, confl_delete_missing, confl_multiple_unique_conflicts, stats_reset);
 pg_stat_sys_indexes| SELECT relid,
     indexrelid,
     schemaname,
diff --git a/src/test/subscription/meson.build b/src/test/subscription/meson.build
index d40b49714f6..586ffba434e 100644
--- a/src/test/subscription/meson.build
+++ b/src/test/subscription/meson.build
@@ -41,6 +41,7 @@ tests += {
       't/032_subscribe_use_index.pl',
       't/033_run_as_table_owner.pl',
       't/034_temporal.pl',
+      't/035_conflicts.pl',
       't/100_bugs.pl',
     ],
   },
diff --git a/src/test/subscription/t/035_conflicts.pl b/src/test/subscription/t/035_conflicts.pl
new file mode 100644
index 00000000000..f9778db7cc9
--- /dev/null
+++ b/src/test/subscription/t/035_conflicts.pl
@@ -0,0 +1,113 @@
+# Copyright (c) 2025, PostgreSQL Global Development Group
+
+# Test the conflict detection of conflict type 'multiple_unique_conflicts'.
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+###############################
+# Setup
+###############################
+
+# Create a publisher node
+my $node_publisher = PostgreSQL::Test::Cluster->new('publisher');
+$node_publisher->init(allows_streaming => 'logical');
+$node_publisher->start;
+
+# Create a subscriber node
+my $node_subscriber = PostgreSQL::Test::Cluster->new('subscriber');
+$node_subscriber->init;
+$node_subscriber->start;
+
+# Create a table on publisher
+$node_publisher->safe_psql('postgres',
+	"CREATE TABLE conf_tab (a int PRIMARY KEY, b int UNIQUE, c int UNIQUE);");
+
+# Create same table on subscriber
+$node_subscriber->safe_psql('postgres',
+	"CREATE TABLE conf_tab (a int PRIMARY key, b int UNIQUE, c int UNIQUE);");
+
+# Setup logical replication
+my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres';
+$node_publisher->safe_psql('postgres',
+	"CREATE PUBLICATION pub_tab FOR TABLE conf_tab");
+
+# Create the subscription
+my $appname = 'sub_tab';
+$node_subscriber->safe_psql(
+	'postgres',
+	"CREATE SUBSCRIPTION sub_tab
+	 CONNECTION '$publisher_connstr application_name=$appname'
+	 PUBLICATION pub_tab;");
+
+# Wait for initial table sync to finish
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname);
+
+##################################################
+# INSERT data on Pub and Sub
+##################################################
+
+# Insert data in the publisher table
+$node_publisher->safe_psql('postgres',
+	"INSERT INTO conf_tab VALUES (1,1,1);");
+
+# Insert data in the subscriber table
+$node_subscriber->safe_psql('postgres',
+	"INSERT INTO conf_tab VALUES (2,2,2), (3,3,3), (4,4,4);");
+
+##################################################
+# Test multiple_unique_conflicts due to INSERT
+##################################################
+my $log_offset = -s $node_subscriber->logfile;
+
+$node_publisher->safe_psql('postgres',
+	"INSERT INTO conf_tab VALUES (2,3,4);");
+
+# Confirm that this causes an error on the subscriber
+$node_subscriber->wait_for_log(
+	qr/conflict detected on relation \"public.conf_tab\": conflict=multiple_unique_conflicts.*
+.*Key already exists in unique index \"conf_tab_pkey\".*
+.*Key \(a\)=\(2\); existing local tuple \(2, 2, 2\); remote tuple \(2, 3, 4\).*
+.*Key already exists in unique index \"conf_tab_b_key\".*
+.*Key \(b\)=\(3\); existing local tuple \(3, 3, 3\); remote tuple \(2, 3, 4\).*
+.*Key already exists in unique index \"conf_tab_c_key\".*
+.*Key \(c\)=\(4\); existing local tuple \(4, 4, 4\); remote tuple \(2, 3, 4\)./,
+	$log_offset);
+
+pass('multiple_unique_conflicts detected during update');
+
+# Truncate table to get rid of the error
+$node_subscriber->safe_psql('postgres', "TRUNCATE conf_tab;");
+
+##################################################
+# Test multiple_unique_conflicts due to UPDATE
+##################################################
+$log_offset = -s $node_subscriber->logfile;
+
+# Insert data in the publisher table
+$node_publisher->safe_psql('postgres',
+	"INSERT INTO conf_tab VALUES (5,5,5);");
+
+# Insert data in the subscriber table
+$node_subscriber->safe_psql('postgres',
+	"INSERT INTO conf_tab VALUES (6,6,6), (7,7,7), (8,8,8);");
+
+$node_publisher->safe_psql('postgres',
+	"UPDATE conf_tab set a=6, b=7, c=8 where a=5;");
+
+# Confirm that this causes an error on the subscriber
+$node_subscriber->wait_for_log(
+	qr/conflict detected on relation \"public.conf_tab\": conflict=multiple_unique_conflicts.*
+.*Key already exists in unique index \"conf_tab_pkey\".*
+.*Key \(a\)=\(6\); existing local tuple \(6, 6, 6\); remote tuple \(6, 7, 8\).*
+.*Key already exists in unique index \"conf_tab_b_key\".*
+.*Key \(b\)=\(7\); existing local tuple \(7, 7, 7\); remote tuple \(6, 7, 8\).*
+.*Key already exists in unique index \"conf_tab_c_key\".*
+.*Key \(c\)=\(8\); existing local tuple \(8, 8, 8\); remote tuple \(6, 7, 8\)./,
+	$log_offset);
+
+pass('multiple_unique_conflicts detected during insert');
+
+done_testing();