public inbox for [email protected]
help / color / mirror / Atom feedFrom: Aya Iwata (Fujitsu) <[email protected]>
To: 'Michael Paquier' <[email protected]>
To: Hayato Kuroda (Fujitsu) <[email protected]>
Cc: pgsql-hackers <[email protected]>
Subject: RE: [PROPOSAL] Termination of Background Workers for ALTER/DROP DATABASE
Date: Mon, 6 Oct 2025 11:21:02 +0000
Message-ID: <OS7PR01MB119648846BA926C096CE016B6EAE3A@OS7PR01MB11964.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <[email protected]>
References: <OS7PR01MB11964335F36BE41021B62EAE8EAE4A@OS7PR01MB11964.jpnprd01.prod.outlook.com>
<OSCPR01MB149662AEA64F4E66F494C2584F5E3A@OSCPR01MB14966.jpnprd01.prod.outlook.com>
<[email protected]>
Hi,
Thank you for your comments.
> On Mon, Oct 06, 2025 at 01:59:08AM +0000, Hayato Kuroda (Fujitsu) wrote:
> > Per my understanding, we already have a facility that terminates a
> background
> > worker, TerminateBackgroundWorker(). So, I'm afraid your proposal has
> already
> > been done by combining this function and ProcessUtility_hook.
>
> The main take that I am getting here from Iwata-san is that this would
> lead to less code duplication.
Yeah. My company sometimes wrote extensions which uses background workers,
and it was painful to implement the same part every time.
> lead to less code duplication. Another item, which you are not
> mentioning, is that this would be more flexible with bgworkers that
> have been starting dynamically, where shared_preload_libraries may not
> be used, still a bgworker would need to react. So the suggestion of a
> new API to control if a bgworker should be stopped like any other
> backend when there is a database activity worth it is a good one, as
> long as it is in line with what we do with normal backends.
Thanks for the agreement. Thus I want to proceed the patch.
> AcceptBackgroundWorkerCancel() is going backwards, IMO. Wouldn't it
> be better to pass it down as an option in bgw_flags, to mark that a
> bgworker connected to a database can be shutdown due to the effect of
> a database getting dropped or moved? There could be an argument
> behind using bgw_extra, but that would not be in line with the
> database connection argument which is a state defined when a bgworker
> is registered.
I updated my patch using bgw_flags to set whether accept to terminate bgworker or not.
And I also removed AcceptBackgroundWorkerCancel() function.
Please check my attached patch.
>
> > So, is the main benefit of the patch to shorten extensions codes which uses
> > bgworker?
>
> I'd ask for the addition of tests when it comes to such a facility,
> and your proposal has none of that. I would suggest worker_spi with
> an option that can be passed to worker_spi_launch().
I added the TAP test using worker_spi too.
Regards,
Aya Iwata
Fujitsu Limited
Attachments:
[application/octet-stream] v0002-0001-Allow-background-workers-to-be-terminated.patch (9.8K, 2-v0002-0001-Allow-background-workers-to-be-terminated.patch)
download | inline diff:
From 172b7df5273d1e90d8d9d550607a17ba6859d197 Mon Sep 17 00:00:00 2001
From: "iwata.aya" <[email protected]>
Date: Thu, 11 Sep 2025 21:16:51 +0900
Subject: [PATCH v0002] Allow background workers to be terminated at DROP
DATABASE
---
doc/src/sgml/bgworker.sgml | 17 ++++
src/backend/postmaster/bgworker.c | 49 ++++++++++++
src/backend/storage/ipc/procarray.c | 6 ++
src/include/postmaster/bgworker.h | 16 ++++
src/test/modules/worker_spi/meson.build | 1 +
.../worker_spi/t/002_worker_terminate.pl | 80 +++++++++++++++++++
src/test/modules/worker_spi/worker_spi.c | 7 +-
7 files changed, 174 insertions(+), 2 deletions(-)
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..dd3d529d762 100644
--- a/doc/src/sgml/bgworker.sgml
+++ b/doc/src/sgml/bgworker.sgml
@@ -108,6 +108,23 @@ typedef struct BackgroundWorker
</listitem>
</varlistentry>
+ <varlistentry>
+ <term><literal>BGWORKER_EXIT_AT_DATABASE_DROP</literal></term>
+ <listitem>
+ <para>
+ <indexterm><primary>BGWORKER_EXIT_AT_DATABASE_DROP</primary></indexterm>
+ Requests to terminate background worker when the database connected by
+ the background worker is changed. DBMS damon can issue a termination
+ signal to the background worker.
+ This occurs only when significant changes affecting the entire database
+ take place.
+ Specifically, major changes include when the <command>DROP DATABASE</command>,
+ <command>ALTER DATABASE RENAME TO</command>, and
+ <command>ALTER DATABASE SET TABLESPACE</command> commands are executed.
+ </para>
+ </listitem>
+ </varlistentry>
+
</variablelist>
</para>
diff --git a/src/backend/postmaster/bgworker.c b/src/backend/postmaster/bgworker.c
index 1ad65c237c3..337efca38bd 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 +1397,51 @@ GetBackgroundWorkerTypeByPid(pid_t pid)
return result;
}
+
+
+/*
+ * Cancel background workers.
+ */
+void
+CancelBackgroundWorkers(Oid databaseId, int cancel_flags)
+{
+ int slotno;
+ bool signal_postmaster = false;
+
+ LWLockAcquire(BackgroundWorkerLock, LW_EXCLUSIVE);
+
+ for (slotno = 0; slotno < BackgroundWorkerData->total_slots; ++slotno)
+ {
+ BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
+
+ /* Check worker slot. */
+ if (!slot->in_use)
+ continue;
+
+ /* 1st, check cancel flags. */
+ if ((slot->worker.bgw_flags & BGWORKER_EXIT_AT_DATABASE_DROP) & cancel_flags)
+ {
+ PGPROC *proc = BackendPidGetProc(slot->pid);
+
+ if (!proc)
+ continue;
+
+ /* 2nd, compare databaseId. */
+ if (proc->databaseId == databaseId)
+ {
+ /*
+ * Set terminate flag in shared memory, unless slot has
+ * been reused.
+ */
+ 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..36571354324 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 +3769,11 @@ CountOtherDBBackends(Oid databaseId, int *nbackends, int *nprepared)
for (index = 0; index < nautovacs; index++)
(void) kill(autovac_pids[index], SIGTERM); /* ignore any error */
+ /*
+ * Cancel background workers by admin commands.
+ */
+ CancelBackgroundWorkers(databaseId, BGWORKER_CANCEL_ADMIN_COMMANDS);
+
/* 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..637cd753c22 100644
--- a/src/include/postmaster/bgworker.h
+++ b/src/include/postmaster/bgworker.h
@@ -59,6 +59,14 @@
*/
#define BGWORKER_BACKEND_DATABASE_CONNECTION 0x0002
+/*
+ * This flag means the bgworker must be exit when the connecting database is
+ * being dropped or moved.
+ * It requires both BGWORKER_SHMEM_ACCESS and
+ * BGWORKER_BACKEND_DATABASE_CONNECTION were passed too.
+ */
+#define BGWORKER_EXIT_AT_DATABASE_DROP 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
@@ -68,6 +76,11 @@
#define BGWORKER_CLASS_PARALLEL 0x0010
/* add additional bgworker classes here */
+/*
+ * Flags for cancel by admin commands.
+ */
+#define BGWORKER_CANCEL_NOACCEPT 0x0000
+#define BGWORKER_CANCEL_ADMIN_COMMANDS 0x0004
typedef void (*bgworker_main_type) (Datum main_arg);
@@ -161,4 +174,7 @@ extern void BackgroundWorkerInitializeConnectionByOid(Oid dboid, Oid useroid, ui
extern void BackgroundWorkerBlockSignals(void);
extern void BackgroundWorkerUnblockSignals(void);
+/* Cancel background workers. */
+extern void CancelBackgroundWorkers(Oid databaseId, int cancel_flags);
+
#endif /* BGWORKER_H */
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..78dcd40ae34
--- /dev/null
+++ b/src/test/modules/worker_spi/t/002_worker_terminate.pl
@@ -0,0 +1,80 @@
+# Copyright (c) 2023-2025, PostgreSQL Global Development Group
+
+# Test background workers can be terminated when ALTER/DROP DATABASE happens
+
+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) = @_;
+
+ # Launch a background worker on the given database
+ my $result = $node->safe_psql(
+ $database, qq(
+ SELECT worker_spi_launch(4, oid) IS NOT NULL
+ FROM pg_database WHERE datname = '$database';
+ ));
+ is($result, 't', "dynamic bgworker launched");
+
+ # Check the worker is running correctly
+ $result = $node->safe_psql('postgres',
+ "SELECT count(1) FROM pg_stat_activity WHERE datname = '$database' AND backend_type = 'worker_spi dynamic';"
+ );
+ is($result, 1, 'dynamic bgworker has exist');
+}
+
+# Run the given query and verify the background worker can be terminated
+sub run_db_command
+{
+ my ($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;
+$node->start;
+
+# Create another database. "postgres" is still used to run db commands and
+# checks the pg_stat_activity.
+$node->safe_psql('postgres', 'CREATE DATABASE testdb');
+$node->safe_psql('testdb', 'CREATE EXTENSION worker_spi;');
+
+launch_bgworker($node, 'testdb');
+
+# Testcase 1: ALTER DATABASE SET TABLESPACE
+run_db_command(
+ $node,
+ "ALTER DATABASE testdb RENAME TO renameddb",
+ "ALTER DATABASE SET TABLESPACE");
+
+# Preparation for the next test; create another tablespace
+my $basedir = $node->basedir();
+my $tablespace = "$basedir/tablespace";
+mkdir($tablespace);
+$node->safe_psql('postgres',
+ "CREATE TABLESPACE test_tablespace LOCATION '$tablespace'");
+launch_bgworker($node, 'renameddb');
+
+# Testcase 2: ALTER DATABASE SET TABLESPACE
+run_db_command(
+ $node,
+ "ALTER DATABASE renameddb SET TABLESPACE test_tablespace",
+ "ALTER DATABASE SET TABLESPACE");
+
+launch_bgworker($node, 'renameddb');
+
+# Testcase 2: DROP DATABASE
+run_db_command($node, "DROP DATABASE renameddb", "DROP DATABASE");
+
+done_testing();
diff --git a/src/test/modules/worker_spi/worker_spi.c b/src/test/modules/worker_spi/worker_spi.c
index bea8339f464..02bed2ac110 100644
--- a/src/test/modules/worker_spi/worker_spi.c
+++ b/src/test/modules/worker_spi/worker_spi.c
@@ -128,6 +128,7 @@ initialize_worker_spi(worktable *table)
CommitTransactionCommand();
debug_query_string = NULL;
pgstat_report_activity(STATE_IDLE, NULL);
+
}
void
@@ -361,7 +362,8 @@ _PG_init(void)
/* set up common data for all our workers */
memset(&worker, 0, sizeof(worker));
worker.bgw_flags = BGWORKER_SHMEM_ACCESS |
- BGWORKER_BACKEND_DATABASE_CONNECTION;
+ BGWORKER_BACKEND_DATABASE_CONNECTION |
+ BGWORKER_EXIT_AT_DATABASE_DROP;
worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
worker.bgw_restart_time = BGW_NEVER_RESTART;
sprintf(worker.bgw_library_name, "worker_spi");
@@ -407,7 +409,8 @@ worker_spi_launch(PG_FUNCTION_ARGS)
memset(&worker, 0, sizeof(worker));
worker.bgw_flags = BGWORKER_SHMEM_ACCESS |
- BGWORKER_BACKEND_DATABASE_CONNECTION;
+ BGWORKER_BACKEND_DATABASE_CONNECTION |
+ BGWORKER_EXIT_AT_DATABASE_DROP;
worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
worker.bgw_restart_time = BGW_NEVER_RESTART;
sprintf(worker.bgw_library_name, "worker_spi");
--
2.39.3
view thread (67+ messages) latest in thread
reply
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: [email protected]
Cc: [email protected], [email protected], [email protected]
Subject: RE: [PROPOSAL] Termination of Background Workers for ALTER/DROP DATABASE
In-Reply-To: <OS7PR01MB119648846BA926C096CE016B6EAE3A@OS7PR01MB11964.jpnprd01.prod.outlook.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox