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help / color / mirror / Atom feedFrom: Aya Iwata (Fujitsu) <[email protected]>
To: 'Peter Smith' <[email protected]>
Cc: Chao Li <[email protected]>
Cc: Hayato Kuroda (Fujitsu) <[email protected]>
Cc: Michael Paquier <[email protected]>
Cc: pgsql-hackers <[email protected]>
Subject: RE: [PROPOSAL] Termination of Background Workers for ALTER/DROP DATABASE
Date: Wed, 15 Oct 2025 02:48:43 +0000
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Hi Peter san,
Thank you for your comments. I updated this patch to v0007.
> -----Original Message-----
> From: Peter Smith <[email protected]>
> Sent: Monday, October 13, 2025 10:20 AM
> To: Iwata, Aya/岩田 彩 <[email protected]>
> Cc: Chao Li <[email protected]>; Kuroda, Hayato/黒田 隼人
> <[email protected]>; Michael Paquier <[email protected]>;
> pgsql-hackers <[email protected]>
> Subject: Re: [PROPOSAL] Termination of Background Workers for
> ALTER/DROP DATABASE
>
> On Mon, Oct 13, 2025 at 9:28 AM Peter Smith <[email protected]>
> wrote:
> >
> > Hi Iwata-San,
> >
> > Some v6 comments.
> >
> > ======
> > doc/src/sgml/bgworker.sgml
> >
> > 1.
> > + <para>
> > +
> <indexterm><primary>BGWORKER_EXIT_AT_DATABASE_CHANGE</primar
> y></indexterm>
> > + Requests termination of the background worker when its
> > connected database
> > + is dropped, renamed, or moved to a different tablespace.
> > + In these cases, the postmaster will send a termination signal to the
> > + background worker when any of the following commands are
> executed:
> > + <command>DROP DATABASE</command>,
> > + <command>ALTER DATABASE RENAME TO</command>,
> > + <command>ALTER DATABASE SET TABLESPACE</command>,
> or
> > + <command>CREATE DATABASE</command> (when the worker
> is connected to the
> > + template database).
> > + This flag requires both
> <literal>BGWORKER_SHMEM_ACCESS</literal> and
> > +
> <literal>BGWORKER_BACKEND_DATABASE_CONNECTION</literal>.
> > + </para>
> >
> >
> > IMO, below is an improved wording for this:
> >
> > <para>
> >
> <indexterm><primary>BGWORKER_EXIT_AT_DATABASE_CHANGE</primar
> y></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>
I updated this .sgml file. Thank you for your advice!
> > ======
> > src/backend/postmaster/bgworker.c
> >
> > +
> > +
> > +/*
> > + * Terminate all background workers connected to the given database, if
> they
> > + * had requested it.
> > + */
> > +void
> > +TerminateBackgroundWorkersByOid(Oid databaseId)
> >
> > Only 1 blank line is needed here.
I added 1 blank here.
> > ======
> > src/include/postmaster/bgworker.h
> >
> > +/*
> > + * Exit the bgworker when its database is dropped, renamed, or moved.
> > + * No-op if BGWORKER_BACKEND_DATABASE_CONNECTION is not
> specified.
> > + */
> > +#define BGWORKER_EXIT_AT_DATABASE_CHANGE 0x0004
> > +
> >
> > That double-negative comment seems awkward. IMO, positive statements
> > are clearer. Also, do you think you should mention
> > BGWORKER_SHMEM_ACCESS, or was that deliberately omitted because
> > BGWORKER_BACKEND_DATABASE_CONNECTION requires that?
> >
> > e.g. The suggested comment below is more closely aligned with the
> documentation.
> >
> > SUGGESTION:
> > /*
> > * 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.
> > */
I have replaced this code comment.
> > ======
> > src/test/modules/worker_spi/t/002_worker_terminate.pl
> >
> > +sub launch_bgworker
> > +{
> > + my ($node, $database, $testcase, $allow_terminate) = @_;
> > + my $offset = -s $node->logfile;
> >
> > Would '$request_terminate' be a more correct name for the $allow_terminate
> var?
> >
> > ======
> > src/test/modules/worker_spi/worker_spi.c
> >
> > + bool allow_termination = PG_GETARG_BOOL(4);
> >
> > memset(&worker, 0, sizeof(worker));
> > worker.bgw_flags = BGWORKER_SHMEM_ACCESS |
> > BGWORKER_BACKEND_DATABASE_CONNECTION;
> > +
> > + if (allow_termination)
> > + worker.bgw_flags |= BGWORKER_EXIT_AT_DATABASE_CHANGE;
> > +
> >
> > Would 'request_termination' be a more correct name for this new var?
> >
>
> There's another similar parameter name that I missed in the last post.
> See /src/test/modules/worker_spi/worker_spi--1.0.sql
>
> " allow_termination boolean DEFAULT false)"
I changed these parameter's name to "request_termination".
> On Mon, Oct 13, 2025 at 9:28 AM Peter Smith <[email protected]>
> wrote:
...
> There's another similar parameter name that I missed in the last post.
> See /src/test/modules/worker_spi/worker_spi--1.0.sql
>
> " allow_termination boolean DEFAULT false)"
I also fixed this, too.
Best regards,
Aya Iwata
Fujitsu Limited
Attachments:
[application/octet-stream] v0007-0001-Allow-background-workers-to-be-terminated.patch (10.6K, 2-v0007-0001-Allow-background-workers-to-be-terminated.patch)
download | inline diff:
From b37cba70dc39ebd2a44aa36247dd6a77dec7342d Mon Sep 17 00:00:00 2001
From: "iwata.aya" <[email protected]>
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
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Subject: RE: [PROPOSAL] Termination of Background Workers for ALTER/DROP DATABASE
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