diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index b1c5289fccc..fdf8b3e9c77 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1982,7 +1982,7 @@ include_dir 'conf.d'
Sets the maximum number of background processes that the system
can support. This parameter can only be set at server start. The
- default is 8.
+ default is 16.
@@ -2004,8 +2004,9 @@ include_dir 'conf.d'
Sets the maximum number of workers that can be started by a single
Gather node. Parallel workers are taken from the
pool of processes established by
- . Note that the requested
- number of workers may not actually be available at run time. If this
+ , limited by
+ . Note that the requested
+ number of workers may not actually be available at runtime. If this
occurs, the plan will run with fewer workers than expected, which may
be inefficient. The default value is 2. Setting this value to 0
disables parallel query execution.
@@ -2034,6 +2035,22 @@ include_dir 'conf.d'
+
+ max_parallel_workers (integer)
+
+ max_parallel_workers configuration parameter
+
+
+
+
+ Sets the maximum number of workers that the system can support for
+ parallel queries. The default value is 8. When increasing or
+ decreasing this value, consider also adjusting
+ .
+
+
+
+
backend_flush_after (integer)
diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c
index 59dc3949d83..1c32fcd046c 100644
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -454,7 +454,8 @@ LaunchParallelWorkers(ParallelContext *pcxt)
snprintf(worker.bgw_name, BGW_MAXLEN, "parallel worker for PID %d",
MyProcPid);
worker.bgw_flags =
- BGWORKER_SHMEM_ACCESS | BGWORKER_BACKEND_DATABASE_CONNECTION;
+ BGWORKER_SHMEM_ACCESS | BGWORKER_BACKEND_DATABASE_CONNECTION
+ | BGWORKER_CLASS_PARALLEL;
worker.bgw_start_time = BgWorkerStart_ConsistentState;
worker.bgw_restart_time = BGW_NEVER_RESTART;
worker.bgw_main = ParallelWorkerMain;
diff --git a/src/backend/postmaster/bgworker.c b/src/backend/postmaster/bgworker.c
index 92495850db0..13a6e23a142 100644
--- a/src/backend/postmaster/bgworker.c
+++ b/src/backend/postmaster/bgworker.c
@@ -80,9 +80,22 @@ typedef struct BackgroundWorkerSlot
BackgroundWorker worker;
} BackgroundWorkerSlot;
+/*
+ * In order to limit the total number of parallel workers (according to
+ * max_parallel_workers GUC), we maintain the number of active parallel
+ * workers. Since the postmaster cannot take locks, two variables are used for
+ * this purpose: the number of registered parallel workers (modified by the
+ * backends, protected by BackgroundWorkerLock) and the number of terminated
+ * parallel workers (modified only by the postmaster, lockless). The active
+ * number of parallel workers is the number of registered workers minus the
+ * terminated ones. These counters can of course overflow, but it's not
+ * important here since the subtraction will still give the right number.
+ */
typedef struct BackgroundWorkerArray
{
int total_slots;
+ uint32 parallel_register_count;
+ uint32 parallel_terminate_count;
BackgroundWorkerSlot slot[FLEXIBLE_ARRAY_MEMBER];
} BackgroundWorkerArray;
@@ -127,6 +140,8 @@ BackgroundWorkerShmemInit(void)
int slotno = 0;
BackgroundWorkerData->total_slots = max_worker_processes;
+ BackgroundWorkerData->parallel_register_count = 0;
+ BackgroundWorkerData->parallel_terminate_count = 0;
/*
* Copy contents of worker list into shared memory. Record the shared
@@ -267,9 +282,12 @@ BackgroundWorkerStateChange(void)
/*
* We need a memory barrier here to make sure that the load of
- * bgw_notify_pid completes before the store to in_use.
+ * bgw_notify_pid and the update of parallel_terminate_count
+ * complete before the store to in_use.
*/
notify_pid = slot->worker.bgw_notify_pid;
+ if ((slot->worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
+ BackgroundWorkerData->parallel_terminate_count++;
pg_memory_barrier();
slot->pid = 0;
slot->in_use = false;
@@ -370,6 +388,9 @@ ForgetBackgroundWorker(slist_mutable_iter *cur)
Assert(rw->rw_shmem_slot < max_worker_processes);
slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
+ if ((rw->rw_worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
+ BackgroundWorkerData->parallel_terminate_count++;
+
slot->in_use = false;
ereport(DEBUG1,
@@ -824,6 +845,7 @@ RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
{
int slotno;
bool success = false;
+ bool parallel;
uint64 generation = 0;
/*
@@ -840,8 +862,27 @@ RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
if (!SanityCheckBackgroundWorker(worker, ERROR))
return false;
+ parallel = (worker->bgw_flags & BGWORKER_CLASS_PARALLEL) != 0;
+
LWLockAcquire(BackgroundWorkerLock, LW_EXCLUSIVE);
+ /*
+ * If this is a parallel worker, check whether there are already too many
+ * parallel workers; if so, don't register another one. Our view of
+ * parallel_terminate_count may be slightly stale, but that doesn't really
+ * matter: we would have gotten the same result if we'd arrived here
+ * slightly earlier anyway. There's no help for it, either, since the
+ * postmaster must not take locks; a memory barrier wouldn't guarantee
+ * anything useful.
+ */
+ if (parallel && (BackgroundWorkerData->parallel_register_count -
+ BackgroundWorkerData->parallel_terminate_count) >=
+ max_parallel_workers)
+ {
+ LWLockRelease(BackgroundWorkerLock);
+ return false;
+ }
+
/*
* Look for an unused slot. If we find one, grab it.
*/
@@ -856,6 +897,8 @@ RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
slot->generation++;
slot->terminate = false;
generation = slot->generation;
+ if (parallel)
+ BackgroundWorkerData->parallel_register_count++;
/*
* Make sure postmaster doesn't see the slot as in use before it
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index f23208353c3..c564ae396da 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -121,7 +121,8 @@ int replacement_sort_tuples = 150000;
*/
int NBuffers = 1000;
int MaxConnections = 90;
-int max_worker_processes = 8;
+int max_worker_processes = 16;
+int max_parallel_workers = 8;
int MaxBackends = 0;
int VacuumCostPageHit = 1; /* GUC parameters for vacuum */
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 28ebcb6f3fa..4e49d5b79cc 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2477,7 +2477,7 @@ static struct config_int ConfigureNamesInt[] =
NULL,
},
&max_worker_processes,
- 8, 0, MAX_BACKENDS,
+ 16, 0, MAX_BACKENDS,
check_max_worker_processes, NULL, NULL
},
@@ -2664,6 +2664,16 @@ static struct config_int ConfigureNamesInt[] =
NULL, NULL, NULL
},
+ {
+ {"max_parallel_workers", PGC_USERSET, RESOURCES_ASYNCHRONOUS,
+ gettext_noop("Sets the maximum number of parallel workers than can be active at one time."),
+ NULL
+ },
+ &max_parallel_workers,
+ 8, 0, 1024,
+ NULL, NULL, NULL
+ },
+
{
{"autovacuum_work_mem", PGC_SIGHUP, RESOURCES_MEM,
gettext_noop("Sets the maximum memory to be used by each autovacuum worker process."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 0df15380a9a..1f490c7de4f 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -161,8 +161,9 @@
# - Asynchronous Behavior -
#effective_io_concurrency = 1 # 1-1000; 0 disables prefetching
-#max_worker_processes = 8 # (change requires restart)
+#max_worker_processes = 16 # (change requires restart)
#max_parallel_workers_per_gather = 2 # taken from max_worker_processes
+#max_parallel_workers = 8 # total maximum number of worker_processes
#old_snapshot_threshold = -1 # 1min-60d; -1 disables; 0 is immediate
# (change requires restart)
#backend_flush_after = 0 # measured in pages, 0 disables
diff --git a/src/bin/pg_resetxlog/pg_resetxlog.c b/src/bin/pg_resetxlog/pg_resetxlog.c
index 2b76f640797..1beee7f8eb8 100644
--- a/src/bin/pg_resetxlog/pg_resetxlog.c
+++ b/src/bin/pg_resetxlog/pg_resetxlog.c
@@ -584,7 +584,7 @@ GuessControlValues(void)
ControlFile.wal_log_hints = false;
ControlFile.track_commit_timestamp = false;
ControlFile.MaxConnections = 100;
- ControlFile.max_worker_processes = 8;
+ ControlFile.max_worker_processes = 16;
ControlFile.max_prepared_xacts = 0;
ControlFile.max_locks_per_xact = 64;
@@ -800,7 +800,7 @@ RewriteControlFile(void)
ControlFile.wal_log_hints = false;
ControlFile.track_commit_timestamp = false;
ControlFile.MaxConnections = 100;
- ControlFile.max_worker_processes = 8;
+ ControlFile.max_worker_processes = 16;
ControlFile.max_prepared_xacts = 0;
ControlFile.max_locks_per_xact = 64;
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 78c99543656..d06eca54b46 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -157,6 +157,7 @@ extern PGDLLIMPORT int NBuffers;
extern int MaxBackends;
extern int MaxConnections;
extern int max_worker_processes;
+extern int max_parallel_workers;
extern PGDLLIMPORT int MyProcPid;
extern PGDLLIMPORT pg_time_t MyStartTime;
diff --git a/src/include/postmaster/bgworker.h b/src/include/postmaster/bgworker.h
index b6889a33200..b46d5818e79 100644
--- a/src/include/postmaster/bgworker.h
+++ b/src/include/postmaster/bgworker.h
@@ -58,6 +58,15 @@
*/
#define BGWORKER_BACKEND_DATABASE_CONNECTION 0x0002
+/*
+ * 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
+ * max_parallel_workers parallel workers at the same time. Third party
+ * background workers should not use this class.
+ */
+#define BGWORKER_CLASS_PARALLEL 0x0010
+/* add additional bgworker classes here */
+
typedef void (*bgworker_main_type) (Datum main_arg);