v0007-0001-Allow-background-workers-to-be-terminated.patch

From b37cba70dc39ebd2a44aa36247dd6a77dec7342d Mon Sep 17 00:00:00 2001
From: "iwata.aya" <iwata.aya@fujitsu.com>
Date: Thu, 11 Sep 2025 21:16:51 +0900
Subject: [PATCH v0007] Allow background workers to be terminated at DROP
 DATABASE

---
 doc/src/sgml/bgworker.sgml                    |  19 ++++
 src/backend/postmaster/bgworker.c             |  41 +++++++
 src/backend/storage/ipc/procarray.c           |   7 ++
 src/include/postmaster/bgworker.h             |   8 ++
 src/test/modules/worker_spi/meson.build       |   1 +
 .../worker_spi/t/002_worker_terminate.pl      | 106 ++++++++++++++++++
 .../modules/worker_spi/worker_spi--1.0.sql    |   3 +-
 src/test/modules/worker_spi/worker_spi.c      |   5 +
 8 files changed, 189 insertions(+), 1 deletion(-)
 create mode 100644 src/test/modules/worker_spi/t/002_worker_terminate.pl

diff --git a/doc/src/sgml/bgworker.sgml b/doc/src/sgml/bgworker.sgml
index 2c393385a91..6f4fc57e3d9 100644
--- a/doc/src/sgml/bgworker.sgml
+++ b/doc/src/sgml/bgworker.sgml
@@ -108,6 +108,25 @@ typedef struct BackgroundWorker
      </listitem>
     </varlistentry>
 
+    <varlistentry>
+     <term><literal>BGWORKER_EXIT_AT_DATABASE_CHANGE</literal></term>
+     <listitem>
+     <para>
+      <indexterm><primary>BGWORKER_EXIT_AT_DATABASE_CHANGE</primary></indexterm>
+      Requests termination of the background worker when its connected database is
+      dropped, renamed, moved to a different tablespace, or used as a template for
+      <command>CREATE DATABASE</command>. Specifically, the postmaster sends a
+      termination signal when any of these commands affect the worker's database:
+      <command>DROP DATABASE</command>,
+      <command>ALTER DATABASE RENAME TO</command>,
+      <command>ALTER DATABASE SET TABLESPACE</command>, or
+      <command>CREATE DATABASE</command>.
+      Requires both <literal>BGWORKER_SHMEM_ACCESS</literal> and
+      <literal>BGWORKER_BACKEND_DATABASE_CONNECTION</literal>.
+     </para>
+     </listitem>
+    </varlistentry>
+
    </variablelist>
 
   </para>
diff --git a/src/backend/postmaster/bgworker.c b/src/backend/postmaster/bgworker.c
index 1ad65c237c3..92600e59011 100644
--- a/src/backend/postmaster/bgworker.c
+++ b/src/backend/postmaster/bgworker.c
@@ -26,6 +26,7 @@
 #include "storage/lwlock.h"
 #include "storage/pmsignal.h"
 #include "storage/proc.h"
+#include "storage/procarray.h"
 #include "storage/procsignal.h"
 #include "storage/shmem.h"
 #include "tcop/tcopprot.h"
@@ -1396,3 +1397,43 @@ GetBackgroundWorkerTypeByPid(pid_t pid)
 
 	return result;
 }
+
+/*
+ * Terminate all background workers connected to the given database, if they
+ * had requested it.
+ */
+
+void
+TerminateBackgroundWorkersByOid(Oid databaseId)
+{
+	bool		signal_postmaster = false;
+
+	LWLockAcquire(BackgroundWorkerLock, LW_EXCLUSIVE);
+
+	/*
+	 * Iterate through slots, looking for workers connected to the given
+	 * database.
+	 */
+	for (int slotno = 0; slotno < BackgroundWorkerData->total_slots; ++slotno)
+	{
+		BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
+
+		if (slot->in_use &&
+			(slot->worker.bgw_flags & BGWORKER_EXIT_AT_DATABASE_CHANGE))
+		{
+			PGPROC	   *proc = BackendPidGetProc(slot->pid);
+
+			if (proc && proc->databaseId == databaseId)
+			{
+				slot->terminate = true;
+				signal_postmaster = true;
+			}
+		}
+	}
+
+	LWLockRelease(BackgroundWorkerLock);
+
+	/* Make sure the postmaster notices the change to shared memory. */
+	if (signal_postmaster)
+		SendPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE);
+}
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 200f72c6e25..2d31c71fd8e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -56,6 +56,7 @@
 #include "catalog/pg_authid.h"
 #include "miscadmin.h"
 #include "pgstat.h"
+#include "postmaster/bgworker.h"
 #include "port/pg_lfind.h"
 #include "storage/proc.h"
 #include "storage/procarray.h"
@@ -3768,6 +3769,12 @@ CountOtherDBBackends(Oid databaseId, int *nbackends, int *nprepared)
 		for (index = 0; index < nautovacs; index++)
 			(void) kill(autovac_pids[index], SIGTERM);	/* ignore any error */
 
+		/*
+		 * Terminate all background workers for this database, if they had
+		 * requested it (BGWORKER_EXIT_AT_DATABASE_CHANGE)
+		 */
+		TerminateBackgroundWorkersByOid(databaseId);
+
 		/* sleep, then try again */
 		pg_usleep(100 * 1000L); /* 100ms */
 	}
diff --git a/src/include/postmaster/bgworker.h b/src/include/postmaster/bgworker.h
index 058667a47a0..a392f190bd4 100644
--- a/src/include/postmaster/bgworker.h
+++ b/src/include/postmaster/bgworker.h
@@ -59,6 +59,13 @@
  */
 #define BGWORKER_BACKEND_DATABASE_CONNECTION		0x0002
 
+/*
+ * Exit the bgworker when its database is dropped, renamed, moved to a
+ * different tablespace, or used as a template for CREATE DATABASE.
+ * Requires BGWORKER_SHMEM_ACCESS and BGWORKER_BACKEND_DATABASE_CONNECTION.
+ */
+#define BGWORKER_EXIT_AT_DATABASE_CHANGE		0x0004
+
 /*
  * This class is used internally for parallel queries, to keep track of the
  * number of active parallel workers and make sure we never launch more than
@@ -128,6 +135,7 @@ extern const char *GetBackgroundWorkerTypeByPid(pid_t pid);
 
 /* Terminate a bgworker */
 extern void TerminateBackgroundWorker(BackgroundWorkerHandle *handle);
+extern void TerminateBackgroundWorkersByOid(Oid databaseId);
 
 /* This is valid in a running worker */
 extern PGDLLIMPORT BackgroundWorker *MyBgworkerEntry;
diff --git a/src/test/modules/worker_spi/meson.build b/src/test/modules/worker_spi/meson.build
index d673ece48a0..1d30048aec8 100644
--- a/src/test/modules/worker_spi/meson.build
+++ b/src/test/modules/worker_spi/meson.build
@@ -28,6 +28,7 @@ tests += {
   'tap': {
     'tests': [
       't/001_worker_spi.pl',
+      't/002_worker_terminate.pl'
     ],
   },
 }
diff --git a/src/test/modules/worker_spi/t/002_worker_terminate.pl b/src/test/modules/worker_spi/t/002_worker_terminate.pl
new file mode 100644
index 00000000000..979ad80651c
--- /dev/null
+++ b/src/test/modules/worker_spi/t/002_worker_terminate.pl
@@ -0,0 +1,106 @@
+# Copyright (c) 2023-2025, PostgreSQL Global Development Group
+
+# Test background workers can be terminated
+
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Ensure the worker_spi dynamic worker is launched on the specified database
+sub launch_bgworker
+{
+	my ($node, $database, $testcase, $request_terminate) = @_;
+	my $offset = -s $node->logfile;
+
+	# Launch a background worker on the given database
+	my $result = $node->safe_psql(
+		$database, qq(
+        SELECT worker_spi_launch($testcase, oid, 0, '{}', $request_terminate) IS NOT NULL
+        FROM pg_database WHERE datname = '$database';
+    ));
+	is($result, 't', "dynamic bgworker launched");
+
+	# Check the worker is surely initialized
+	$node->wait_for_log(
+		qr/LOG:  worker_spi dynamic worker $testcase initialized with .*\..*/,
+		$offset);
+}
+
+# Run the given query and verify the background worker can be terminated
+sub run_db_command
+{
+	my ($node, $command, $testname) = @_;
+	my $offset = -s $node->logfile;
+
+	$node->safe_psql('postgres', $command);
+	ok( $node->log_contains(
+			"terminating background worker \"worker_spi dynamic\" due to administrator command",
+			$offset),
+		"background worker can be terminated at $testname");
+}
+
+my $node = PostgreSQL::Test::Cluster->new('mynode');
+$node->init;
+$node->start;
+
+$node->safe_psql('postgres', 'CREATE EXTENSION worker_spi;');
+
+# Launch a background worker without BGWORKER_EXIT_AT_DATABASE_CHANGE
+launch_bgworker($node, 'postgres', 0, "false");
+
+# Ensure CREATE DATABASE WITH TEMPLATE fails because background worker retains
+#
+# XXX This spends more than 5 seconds because the backend retries counting
+# number of connecting processes 50 times. See CountOtherDBBackends().
+my $stderr;
+
+$node->psql(
+	'postgres',
+	"CREATE DATABASE testdb WITH TEMPLATE postgres",
+	stderr => \$stderr);
+ok( $stderr =~
+	  "source database \"postgres\" is being accessed by other users",
+	"background worker blocked the database creation");
+
+# Terminate the background worker for upcoming tests
+$node->safe_psql(
+	"postgres", qq(
+        SELECT pg_terminate_backend(pid)
+        FROM pg_stat_activity WHERE backend_type = 'worker_spi dynamic';));
+
+# Ensure BGWORKER_EXIT_AT_DATABASE_CHANGE allows background workers to be
+# terminated at some database manipulations.
+#
+# Testcase 1: CREATE DATABASE WITH TEMPLATE
+launch_bgworker($node, 'postgres', 1, "true");
+run_db_command(
+	$node,
+	"CREATE DATABASE testdb WITH TEMPLATE postgres",
+	"CREATE DATABASE WITH TEMPLATE");
+
+# Testcase 2: ALTER DATABASE RENAME
+launch_bgworker($node, 'testdb', 2, "true");
+run_db_command(
+	$node,
+	"ALTER DATABASE testdb RENAME TO renameddb",
+	"ALTER DATABASE RENAME");
+
+# Preparation for the next test; create another tablespace
+my $tablespace = PostgreSQL::Test::Utils::tempdir;
+$node->safe_psql('postgres',
+	"CREATE TABLESPACE test_tablespace LOCATION '$tablespace'");
+
+# Testcase 3: ALTER DATABASE SET TABLESPACE
+launch_bgworker($node, 'renameddb', 3, "true");
+run_db_command(
+	$node,
+	"ALTER DATABASE renameddb SET TABLESPACE test_tablespace",
+	"ALTER DATABASE SET TABLESPACE");
+
+# Testcase 4: DROP DATABASE
+launch_bgworker($node, 'renameddb', 4, "true");
+run_db_command($node, "DROP DATABASE renameddb", "DROP DATABASE");
+
+done_testing();
diff --git a/src/test/modules/worker_spi/worker_spi--1.0.sql b/src/test/modules/worker_spi/worker_spi--1.0.sql
index 84deb6199f6..3d12de37bea 100644
--- a/src/test/modules/worker_spi/worker_spi--1.0.sql
+++ b/src/test/modules/worker_spi/worker_spi--1.0.sql
@@ -7,7 +7,8 @@
 CREATE FUNCTION worker_spi_launch(index int4,
   dboid oid DEFAULT 0,
   roleoid oid DEFAULT 0,
-  flags text[] DEFAULT '{}')
+  flags text[] DEFAULT '{}',
+  request_termination boolean DEFAULT false)
 RETURNS pg_catalog.int4 STRICT
 AS 'MODULE_PATHNAME'
 LANGUAGE C;
diff --git a/src/test/modules/worker_spi/worker_spi.c b/src/test/modules/worker_spi/worker_spi.c
index bea8339f464..2912abe6cce 100644
--- a/src/test/modules/worker_spi/worker_spi.c
+++ b/src/test/modules/worker_spi/worker_spi.c
@@ -404,10 +404,15 @@ worker_spi_launch(PG_FUNCTION_ARGS)
 	Size		ndim;
 	int			nelems;
 	Datum	   *datum_flags;
+	bool		request_termination = PG_GETARG_BOOL(4);
 
 	memset(&worker, 0, sizeof(worker));
 	worker.bgw_flags = BGWORKER_SHMEM_ACCESS |
 		BGWORKER_BACKEND_DATABASE_CONNECTION;
+
+	if (request_termination)
+		worker.bgw_flags |= BGWORKER_EXIT_AT_DATABASE_CHANGE;
+
 	worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
 	worker.bgw_restart_time = BGW_NEVER_RESTART;
 	sprintf(worker.bgw_library_name, "worker_spi");
-- 
2.39.3