On Fri, May 03, 2024 at 12:57:18PM +0000, Imseih (AWS), Sami wrote:
>> That's true, but using a hard-coded limit means we no longer need to add a
>> new GUC. Always allocating, say, 256 slots might require a few additional
>> kilobytes of shared memory, most of which will go unused, but that seems
>> unlikely to be a problem for the systems that will run Postgres v18.
>
> I agree with this.
Here's what this might look like. I chose an upper limit of 1024, which
seems like it "ought to be enough for anybody," at least for now.
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com
>From 72e0496294ef0390c77cef8031ae51c1a44ebde8 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nat...@postgresql.org>
Date: Tue, 7 May 2024 10:59:24 -0500
Subject: [PATCH v3 1/1] allow changing autovacuum_max_workers without
restarting
---
doc/src/sgml/config.sgml | 3 +-
doc/src/sgml/runtime.sgml | 15 ++++---
src/backend/access/transam/xlog.c | 2 +-
src/backend/postmaster/autovacuum.c | 44 ++++++++++++-------
src/backend/postmaster/postmaster.c | 2 +-
src/backend/storage/lmgr/proc.c | 9 ++--
src/backend/utils/init/postinit.c | 20 ++-------
src/backend/utils/misc/guc_tables.c | 7 ++-
src/backend/utils/misc/postgresql.conf.sample | 1 -
src/include/postmaster/autovacuum.h | 8 ++++
src/include/utils/guc_hooks.h | 2 -
11 files changed, 58 insertions(+), 55 deletions(-)
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index e93208b2e6..8e2a1d6902 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -8528,7 +8528,8 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
<para>
Specifies the maximum number of autovacuum processes (other than the
autovacuum launcher) that may be running at any one time. The default
- is three. This parameter can only be set at server start.
+ is three. This parameter can only be set in the
+ <filename>postgresql.conf</filename> file or on the server command line.
</para>
</listitem>
</varlistentry>
diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index 6047b8171d..8a672a8383 100644
--- a/doc/src/sgml/runtime.sgml
+++ b/doc/src/sgml/runtime.sgml
@@ -781,13 +781,13 @@ psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such
<row>
<entry><varname>SEMMNI</varname></entry>
<entry>Maximum number of semaphore identifiers (i.e., sets)</entry>
- <entry>at least <literal>ceil((max_connections + autovacuum_max_workers + max_wal_senders + max_worker_processes + 5) / 16)</literal> plus room for other applications</entry>
+ <entry>at least <literal>ceil((max_connections + max_wal_senders + max_worker_processes + 1029) / 16)</literal> plus room for other applications</entry>
</row>
<row>
<entry><varname>SEMMNS</varname></entry>
<entry>Maximum number of semaphores system-wide</entry>
- <entry><literal>ceil((max_connections + autovacuum_max_workers + max_wal_senders + max_worker_processes + 5) / 16) * 17</literal> plus room for other applications</entry>
+ <entry><literal>ceil((max_connections + max_wal_senders + max_worker_processes + 1029) / 16) * 17</literal> plus room for other applications</entry>
</row>
<row>
@@ -838,7 +838,7 @@ psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such
When using System V semaphores,
<productname>PostgreSQL</productname> uses one semaphore per allowed connection
(<xref linkend="guc-max-connections"/>), allowed autovacuum worker process
- (<xref linkend="guc-autovacuum-max-workers"/>) and allowed background
+ (1024) and allowed background
process (<xref linkend="guc-max-worker-processes"/>), in sets of 16.
Each such set will
also contain a 17th semaphore which contains a <quote>magic
@@ -846,13 +846,14 @@ psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such
other applications. The maximum number of semaphores in the system
is set by <varname>SEMMNS</varname>, which consequently must be at least
as high as <varname>max_connections</varname> plus
- <varname>autovacuum_max_workers</varname> plus <varname>max_wal_senders</varname>,
- plus <varname>max_worker_processes</varname>, plus one extra for each 16
+ <varname>max_wal_senders</varname>,
+ plus <varname>max_worker_processes</varname>, plus 1024 for autovacuum
+ worker processes, plus one extra for each 16
allowed connections plus workers (see the formula in <xref
linkend="sysvipc-parameters"/>). The parameter <varname>SEMMNI</varname>
determines the limit on the number of semaphore sets that can
exist on the system at one time. Hence this parameter must be at
- least <literal>ceil((max_connections + autovacuum_max_workers + max_wal_senders + max_worker_processes + 5) / 16)</literal>.
+ least <literal>ceil((max_connections + max_wal_senders + max_worker_processes + 1029) / 16)</literal>.
Lowering the number
of allowed connections is a temporary workaround for failures,
which are usually confusingly worded <quote>No space
@@ -883,7 +884,7 @@ psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such
When using POSIX semaphores, the number of semaphores needed is the
same as for System V, that is one semaphore per allowed connection
(<xref linkend="guc-max-connections"/>), allowed autovacuum worker process
- (<xref linkend="guc-autovacuum-max-workers"/>) and allowed background
+ (1024) and allowed background
process (<xref linkend="guc-max-worker-processes"/>).
On the platforms where this option is preferred, there is no specific
kernel limit on the number of POSIX semaphores.
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index c3fd9c1eae..5b0312b2a6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5362,7 +5362,7 @@ CheckRequiredParameterValues(void)
*/
if (ArchiveRecoveryRequested && EnableHotStandby)
{
- /* We ignore autovacuum_max_workers when we make this test. */
+ /* We ignore autovacuum workers when we make this test. */
RecoveryRequiresIntParameter("max_connections",
MaxConnections,
ControlFile->MaxConnections);
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 9a925a10cd..1ab97b9903 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -208,8 +208,7 @@ typedef struct autovac_table
/*-------------
* This struct holds information about a single worker's whereabouts. We keep
- * an array of these in shared memory, sized according to
- * autovacuum_max_workers.
+ * an array of these in shared memory.
*
* wi_links entry into free list or running list
* wi_dboid OID of the database this worker is supposed to work on
@@ -289,7 +288,7 @@ typedef struct
{
sig_atomic_t av_signal[AutoVacNumSignals];
pid_t av_launcherpid;
- dlist_head av_freeWorkers;
+ dclist_head av_freeWorkers;
dlist_head av_runningWorkers;
WorkerInfo av_startingWorker;
AutoVacuumWorkItem av_workItems[NUM_WORKITEMS];
@@ -347,6 +346,7 @@ static void autovac_report_activity(autovac_table *tab);
static void autovac_report_workitem(AutoVacuumWorkItem *workitem,
const char *nspname, const char *relname);
static void avl_sigusr2_handler(SIGNAL_ARGS);
+static bool av_worker_available(void);
@@ -575,8 +575,7 @@ AutoVacLauncherMain(char *startup_data, size_t startup_data_len)
* wakening conditions.
*/
- launcher_determine_sleep(!dlist_is_empty(&AutoVacuumShmem->av_freeWorkers),
- false, &nap);
+ launcher_determine_sleep(av_worker_available(), false, &nap);
/*
* Wait until naptime expires or we get some type of signal (all the
@@ -636,7 +635,7 @@ AutoVacLauncherMain(char *startup_data, size_t startup_data_len)
current_time = GetCurrentTimestamp();
LWLockAcquire(AutovacuumLock, LW_SHARED);
- can_launch = !dlist_is_empty(&AutoVacuumShmem->av_freeWorkers);
+ can_launch = av_worker_available();
if (AutoVacuumShmem->av_startingWorker != NULL)
{
@@ -679,8 +678,8 @@ AutoVacLauncherMain(char *startup_data, size_t startup_data_len)
worker->wi_sharedrel = false;
worker->wi_proc = NULL;
worker->wi_launchtime = 0;
- dlist_push_head(&AutoVacuumShmem->av_freeWorkers,
- &worker->wi_links);
+ dclist_push_head(&AutoVacuumShmem->av_freeWorkers,
+ &worker->wi_links);
AutoVacuumShmem->av_startingWorker = NULL;
ereport(WARNING,
errmsg("autovacuum worker took too long to start; canceled"));
@@ -1087,7 +1086,7 @@ do_start_worker(void)
/* return quickly when there are no free workers */
LWLockAcquire(AutovacuumLock, LW_SHARED);
- if (dlist_is_empty(&AutoVacuumShmem->av_freeWorkers))
+ if (!av_worker_available())
{
LWLockRelease(AutovacuumLock);
return InvalidOid;
@@ -1240,7 +1239,7 @@ do_start_worker(void)
* Get a worker entry from the freelist. We checked above, so there
* really should be a free slot.
*/
- wptr = dlist_pop_head_node(&AutoVacuumShmem->av_freeWorkers);
+ wptr = dclist_pop_head_node(&AutoVacuumShmem->av_freeWorkers);
worker = dlist_container(WorkerInfoData, wi_links, wptr);
worker->wi_dboid = avdb->adw_datid;
@@ -1609,8 +1608,8 @@ FreeWorkerInfo(int code, Datum arg)
MyWorkerInfo->wi_proc = NULL;
MyWorkerInfo->wi_launchtime = 0;
pg_atomic_clear_flag(&MyWorkerInfo->wi_dobalance);
- dlist_push_head(&AutoVacuumShmem->av_freeWorkers,
- &MyWorkerInfo->wi_links);
+ dclist_push_head(&AutoVacuumShmem->av_freeWorkers,
+ &MyWorkerInfo->wi_links);
/* not mine anymore */
MyWorkerInfo = NULL;
@@ -3265,7 +3264,7 @@ AutoVacuumShmemSize(void)
*/
size = sizeof(AutoVacuumShmemStruct);
size = MAXALIGN(size);
- size = add_size(size, mul_size(autovacuum_max_workers,
+ size = add_size(size, mul_size(AUTOVAC_MAX_WORKER_SLOTS,
sizeof(WorkerInfoData)));
return size;
}
@@ -3292,7 +3291,7 @@ AutoVacuumShmemInit(void)
Assert(!found);
AutoVacuumShmem->av_launcherpid = 0;
- dlist_init(&AutoVacuumShmem->av_freeWorkers);
+ dclist_init(&AutoVacuumShmem->av_freeWorkers);
dlist_init(&AutoVacuumShmem->av_runningWorkers);
AutoVacuumShmem->av_startingWorker = NULL;
memset(AutoVacuumShmem->av_workItems, 0,
@@ -3302,10 +3301,10 @@ AutoVacuumShmemInit(void)
MAXALIGN(sizeof(AutoVacuumShmemStruct)));
/* initialize the WorkerInfo free list */
- for (i = 0; i < autovacuum_max_workers; i++)
+ for (i = 0; i < AUTOVAC_MAX_WORKER_SLOTS; i++)
{
- dlist_push_head(&AutoVacuumShmem->av_freeWorkers,
- &worker[i].wi_links);
+ dclist_push_head(&AutoVacuumShmem->av_freeWorkers,
+ &worker[i].wi_links);
pg_atomic_init_flag(&worker[i].wi_dobalance);
}
@@ -3341,3 +3340,14 @@ check_autovacuum_work_mem(int *newval, void **extra, GucSource source)
return true;
}
+
+/*
+ * Returns whether there is a free autovacuum worker slot available.
+ */
+static bool
+av_worker_available(void)
+{
+ int reserved_slots = AUTOVAC_MAX_WORKER_SLOTS - autovacuum_max_workers;
+
+ return dclist_count(&AutoVacuumShmem->av_freeWorkers) > reserved_slots;
+}
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 7f3170a8f0..cab8a8a5f4 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -4144,7 +4144,7 @@ CreateOptsFile(int argc, char *argv[], char *fullprogname)
int
MaxLivePostmasterChildren(void)
{
- return 2 * (MaxConnections + autovacuum_max_workers + 1 +
+ return 2 * (MaxConnections + AUTOVAC_MAX_WORKER_SLOTS + 1 +
max_wal_senders + max_worker_processes);
}
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index e4f256c63c..fdf7373232 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -141,9 +141,8 @@ ProcGlobalSemas(void)
* running out when trying to start another backend is a common failure.
* So, now we grab enough semaphores to support the desired max number
* of backends immediately at initialization --- if the sysadmin has set
- * MaxConnections, max_worker_processes, max_wal_senders, or
- * autovacuum_max_workers higher than his kernel will support, he'll
- * find out sooner rather than later.
+ * MaxConnections, max_worker_processes, or max_wal_senders higher than
+ * his kernel will support, he'll find out sooner rather than later.
*
* Another reason for creating semaphores here is that the semaphore
* implementation typically requires us to create semaphores in the
@@ -242,13 +241,13 @@ InitProcGlobal(void)
dlist_push_tail(&ProcGlobal->freeProcs, &proc->links);
proc->procgloballist = &ProcGlobal->freeProcs;
}
- else if (i < MaxConnections + autovacuum_max_workers + 1)
+ else if (i < MaxConnections + AUTOVAC_MAX_WORKER_SLOTS + 1)
{
/* PGPROC for AV launcher/worker, add to autovacFreeProcs list */
dlist_push_tail(&ProcGlobal->autovacFreeProcs, &proc->links);
proc->procgloballist = &ProcGlobal->autovacFreeProcs;
}
- else if (i < MaxConnections + autovacuum_max_workers + 1 + max_worker_processes)
+ else if (i < MaxConnections + AUTOVAC_MAX_WORKER_SLOTS + 1 + max_worker_processes)
{
/* PGPROC for bgworker, add to bgworkerFreeProcs list */
dlist_push_tail(&ProcGlobal->bgworkerFreeProcs, &proc->links);
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 0805398e24..684b22e3a5 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -577,7 +577,7 @@ InitializeMaxBackends(void)
Assert(MaxBackends == 0);
/* the extra unit accounts for the autovacuum launcher */
- MaxBackends = MaxConnections + autovacuum_max_workers + 1 +
+ MaxBackends = MaxConnections + AUTOVAC_MAX_WORKER_SLOTS + 1 +
max_worker_processes + max_wal_senders;
/* internal error because the values were all checked previously */
@@ -591,19 +591,7 @@ InitializeMaxBackends(void)
bool
check_max_connections(int *newval, void **extra, GucSource source)
{
- if (*newval + autovacuum_max_workers + 1 +
- max_worker_processes + max_wal_senders > MAX_BACKENDS)
- return false;
- return true;
-}
-
-/*
- * GUC check_hook for autovacuum_max_workers
- */
-bool
-check_autovacuum_max_workers(int *newval, void **extra, GucSource source)
-{
- if (MaxConnections + *newval + 1 +
+ if (*newval + AUTOVAC_MAX_WORKER_SLOTS + 1 +
max_worker_processes + max_wal_senders > MAX_BACKENDS)
return false;
return true;
@@ -615,7 +603,7 @@ check_autovacuum_max_workers(int *newval, void **extra, GucSource source)
bool
check_max_worker_processes(int *newval, void **extra, GucSource source)
{
- if (MaxConnections + autovacuum_max_workers + 1 +
+ if (MaxConnections + AUTOVAC_MAX_WORKER_SLOTS + 1 +
*newval + max_wal_senders > MAX_BACKENDS)
return false;
return true;
@@ -627,7 +615,7 @@ check_max_worker_processes(int *newval, void **extra, GucSource source)
bool
check_max_wal_senders(int *newval, void **extra, GucSource source)
{
- if (MaxConnections + autovacuum_max_workers + 1 +
+ if (MaxConnections + AUTOVAC_MAX_WORKER_SLOTS + 1 +
max_worker_processes + *newval > MAX_BACKENDS)
return false;
return true;
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index ea2b0577bc..1e255fe263 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -3380,14 +3380,13 @@ struct config_int ConfigureNamesInt[] =
NULL, NULL, NULL
},
{
- /* see max_connections */
- {"autovacuum_max_workers", PGC_POSTMASTER, AUTOVACUUM,
+ {"autovacuum_max_workers", PGC_SIGHUP, AUTOVACUUM,
gettext_noop("Sets the maximum number of simultaneously running autovacuum worker processes."),
NULL
},
&autovacuum_max_workers,
- 3, 1, MAX_BACKENDS,
- check_autovacuum_max_workers, NULL, NULL
+ 3, 1, AUTOVAC_MAX_WORKER_SLOTS,
+ NULL, NULL, NULL
},
{
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 83d5df8e46..439859e3ff 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -659,7 +659,6 @@
#autovacuum = on # Enable autovacuum subprocess? 'on'
# requires track_counts to also be on.
#autovacuum_max_workers = 3 # max number of autovacuum subprocesses
- # (change requires restart)
#autovacuum_naptime = 1min # time between autovacuum runs
#autovacuum_vacuum_threshold = 50 # min number of row updates before
# vacuum
diff --git a/src/include/postmaster/autovacuum.h b/src/include/postmaster/autovacuum.h
index cae1e8b329..23a7a729aa 100644
--- a/src/include/postmaster/autovacuum.h
+++ b/src/include/postmaster/autovacuum.h
@@ -66,4 +66,12 @@ extern bool AutoVacuumRequestWork(AutoVacuumWorkItemType type,
extern Size AutoVacuumShmemSize(void);
extern void AutoVacuumShmemInit(void);
+/*
+ * Number of autovacuum worker slots to allocate. This is the upper limit of
+ * autovacuum_max_workers.
+ *
+ * NB: This must be less than MAX_BACKENDS.
+ */
+#define AUTOVAC_MAX_WORKER_SLOTS (1024)
+
#endif /* AUTOVACUUM_H */
diff --git a/src/include/utils/guc_hooks.h b/src/include/utils/guc_hooks.h
index d64dc5fcdb..76346eb05e 100644
--- a/src/include/utils/guc_hooks.h
+++ b/src/include/utils/guc_hooks.h
@@ -29,8 +29,6 @@ extern bool check_application_name(char **newval, void **extra,
GucSource source);
extern void assign_application_name(const char *newval, void *extra);
extern const char *show_archive_command(void);
-extern bool check_autovacuum_max_workers(int *newval, void **extra,
- GucSource source);
extern bool check_autovacuum_work_mem(int *newval, void **extra,
GucSource source);
extern bool check_vacuum_buffer_usage_limit(int *newval, void **extra,
--
2.25.1
