From 23e8eb7938546a6b8e767e2ec15c8b3e5315a127 Mon Sep 17 00:00:00 2001
From: reshke <reshke@double.cloud>
Date: Tue, 6 Oct 2026 09:50:11 +0300
Subject: [PATCH v1] reindexdb: error out on index-level REINDEX with
 CONCURRENTLY and multiple jobs

reindexdb batches the REINDEX commands of all indexes attached to the
same table into a single multi-statement query when using multiple jobs,
an oversight of 47f99a407d.  Such a query fails with REINDEX
CONCURRENTLY, as it cannot run inside the implicit transaction block
created for the multi-statement query, and batching cannot be avoided
here because the indexes of one table have to be reindexed one at a
time to avoid conflicts across jobs.

So, error out on this combination instead of attempting a fix.
---
 src/bin/scripts/reindexdb.c        |  8 ++++++++
 src/bin/scripts/t/090_reindexdb.pl | 10 ++++++++++
 2 files changed, 18 insertions(+)

diff --git a/src/bin/scripts/reindexdb.c b/src/bin/scripts/reindexdb.c
index d7fb16d3c85..680a657a37d 100644
--- a/src/bin/scripts/reindexdb.c
+++ b/src/bin/scripts/reindexdb.c
@@ -360,6 +360,14 @@ reindex_one_database(ConnParams *cparams, ReindexType type,
 			case REINDEX_INDEX:
 				Assert(user_list != NULL);
 
+				/*
+				 * Batching the indexes of one table into a single
+				 * multi-statement query does not work with CONCURRENTLY, so
+				 * refuse the combination.
+				 */
+				if (concurrently)
+					pg_fatal("cannot use multiple jobs to reindex indexes concurrently");
+
 				/*
 				 * Generate a list of indexes and a matching list of table
 				 * OIDs, based on the user-specified index names.
diff --git a/src/bin/scripts/t/090_reindexdb.pl b/src/bin/scripts/t/090_reindexdb.pl
index ae7d3724464..b78f31b3795 100644
--- a/src/bin/scripts/t/090_reindexdb.pl
+++ b/src/bin/scripts/t/090_reindexdb.pl
@@ -298,6 +298,16 @@ $node->issues_sql_like(
 	],
 	qr/statement:\ REINDEX TABLE s1.t1;/,
 	'parallel reindexdb for schemas does a per-table REINDEX');
+$node->command_fails(
+	[
+		'reindexdb',
+		'--jobs' => '2',
+		'--concurrently',
+		'--index' => 's1.i1',
+		'--index' => 's2.i2',
+		'postgres',
+	],
+	'parallel reindexdb for indices concurrently');
 $node->command_ok([ 'reindexdb', '--jobs' => '2', '--schema' => 's3' ],
 	'parallel reindexdb with empty schema');
 $node->command_ok(
-- 
2.43.0