global_max_parallel_workers.diff

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index e0e5a1e..c661c7a 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -2018,6 +2018,23 @@ include_dir 'conf.d'
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-parallel-workers" xreflabel="max_parallel_workers">
+       <term><varname>max_parallel_workers</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_parallel_workers</> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Sets the maximum number of workers that can be launched at the same
+         time for the whole server.  This parameter allows the administrator to
+         reserve background worker slots for for third part dynamic background
+         workers.  The default value is 4.  Setting this value to 0 disables
+         parallel query execution.
+        </para>
+       </listitem>
+      </varlistentry>
+
       <varlistentry id="guc-backend-flush-after" xreflabel="backend_flush_after">
        <term><varname>backend_flush_after</varname> (<type>integer</type>)
        <indexterm>
diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c
index ab5ef25..7b53b53 100644
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -473,8 +473,8 @@ LaunchParallelWorkers(ParallelContext *pcxt)
 	{
 		memcpy(worker.bgw_extra, &i, sizeof(int));
 		if (!any_registrations_failed &&
-			RegisterDynamicBackgroundWorker(&worker,
-											&pcxt->worker[i].bgwhandle))
+			RegisterDynamicBackgroundWorkerInternal(&worker,
+											&pcxt->worker[i].bgwhandle, true))
 		{
 			shm_mq_set_handle(pcxt->worker[i].error_mqh,
 							  pcxt->worker[i].bgwhandle);
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index cc8ba61..2bcd86b 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -719,9 +719,11 @@ create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel)
 	}
 
 	/*
-	 * In no case use more than max_parallel_workers_per_gather workers.
+	 * In no case use more than max_parallel_workers or
+	 * max_parallel_workers_per_gather workers.
 	 */
-	parallel_workers = Min(parallel_workers, max_parallel_workers_per_gather);
+	parallel_workers = Min(max_parallel_workers, Min(parallel_workers,
+				max_parallel_workers_per_gather));
 
 	/* If any limit was set to zero, the user doesn't want a parallel scan. */
 	if (parallel_workers <= 0)
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index e7f63f4..fd62126 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -113,6 +113,7 @@ int			effective_cache_size = DEFAULT_EFFECTIVE_CACHE_SIZE;
 
 Cost		disable_cost = 1.0e10;
 
+int			max_parallel_workers = 4;
 int			max_parallel_workers_per_gather = 2;
 
 bool		enable_seqscan = true;
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 54c0440..81d124c 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -246,8 +246,9 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 		IsUnderPostmaster && dynamic_shared_memory_type != DSM_IMPL_NONE &&
 		parse->commandType == CMD_SELECT && !parse->hasModifyingCTE &&
 		parse->utilityStmt == NULL && max_parallel_workers_per_gather > 0 &&
-		!IsParallelWorker() && !IsolationIsSerializable() &&
-		!has_parallel_hazard((Node *) parse, true);
+		max_parallel_workers > 0 && !IsParallelWorker() &&
+		!IsolationIsSerializable() && !has_parallel_hazard((Node *) parse,
+				true);
 
 	/*
 	 * glob->parallelModeNeeded should tell us whether it's necessary to
diff --git a/src/backend/postmaster/bgworker.c b/src/backend/postmaster/bgworker.c
index 382edad..71025b7 100644
--- a/src/backend/postmaster/bgworker.c
+++ b/src/backend/postmaster/bgworker.c
@@ -16,6 +16,7 @@
 
 #include "miscadmin.h"
 #include "libpq/pqsignal.h"
+#include "optimizer/cost.h"
 #include "postmaster/bgworker_internals.h"
 #include "postmaster/postmaster.h"
 #include "storage/barrier.h"
@@ -76,6 +77,7 @@ typedef struct BackgroundWorkerSlot
 	bool		terminate;
 	pid_t		pid;			/* InvalidPid = not started yet; 0 = dead */
 	uint64		generation;		/* incremented when slot is recycled */
+	bool		parallel;
 	BackgroundWorker worker;
 } BackgroundWorkerSlot;
 
@@ -819,12 +821,14 @@ RegisterBackgroundWorker(BackgroundWorker *worker)
  * free this pointer using pfree(), if desired.
  */
 bool
-RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
-								BackgroundWorkerHandle **handle)
+RegisterDynamicBackgroundWorkerInternal(BackgroundWorker *worker,
+								BackgroundWorkerHandle **handle,
+								bool parallel)
 {
 	int			slotno;
 	bool		success = false;
 	uint64		generation = 0;
+	int			n_active_parallel_workers = 0;
 
 	/*
 	 * We can't register dynamic background workers from the postmaster. If
@@ -849,12 +853,22 @@ RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
 	{
 		BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
 
-		if (!slot->in_use)
+		if (slot->in_use && slot->parallel)
+			n_active_parallel_workers++;
+
+		/* In case of parallel worker, check if we didn't exhaust the number of
+		 * allowed parallel workers
+		 */
+		if (parallel && n_active_parallel_workers >= max_parallel_workers)
+			break;
+
+		if(!slot->in_use)
 		{
 			memcpy(&slot->worker, worker, sizeof(BackgroundWorker));
 			slot->pid = InvalidPid;		/* indicates not started yet */
 			slot->generation++;
 			slot->terminate = false;
+			slot->parallel = parallel;
 			generation = slot->generation;
 
 			/*
@@ -888,6 +902,14 @@ RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
 	return success;
 }
 
+bool
+RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
+								BackgroundWorkerHandle **handle)
+{
+	/* public API, not a parallel worker */
+	return RegisterDynamicBackgroundWorkerInternal(worker, handle, false);
+}
+
 /*
  * Get the PID of a dynamically-registered background worker.
  *
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 9b02111..18fa5b5 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2657,6 +2657,16 @@ static struct config_int ConfigureNamesInt[] =
 	},
 
 	{
+		{"max_parallel_workers", PGC_USERSET, RESOURCES_ASYNCHRONOUS,
+			gettext_noop("Sets the maximum number of parallel processes for the cluster."),
+			NULL
+		},
+		&max_parallel_workers,
+		2, 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."),
 			NULL,
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 8260e37..7f16050 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -168,6 +168,7 @@
 #effective_io_concurrency = 1		# 1-1000; 0 disables prefetching
 #max_worker_processes = 8		# (change requires restart)
 #max_parallel_workers_per_gather = 2	# taken from max_worker_processes
+#max_parallel_workers = 4	    # total maximum number of worker_processes
 #old_snapshot_threshold = -1		# 1min-60d; -1 disables; 0 is immediate
 									# (change requires restart)
 #backend_flush_after = 0		# 0 disables, default is 0
diff --git a/src/include/optimizer/cost.h b/src/include/optimizer/cost.h
index f41f9e9..eca5c1e 100644
--- a/src/include/optimizer/cost.h
+++ b/src/include/optimizer/cost.h
@@ -55,6 +55,7 @@ extern PGDLLIMPORT double parallel_setup_cost;
 extern PGDLLIMPORT int effective_cache_size;
 extern Cost disable_cost;
 extern int	max_parallel_workers_per_gather;
+extern int	max_parallel_workers;
 extern bool enable_seqscan;
 extern bool enable_indexscan;
 extern bool enable_indexonlyscan;
diff --git a/src/include/postmaster/bgworker.h b/src/include/postmaster/bgworker.h
index b6889a3..958bc57 100644
--- a/src/include/postmaster/bgworker.h
+++ b/src/include/postmaster/bgworker.h
@@ -107,6 +107,9 @@ extern void RegisterBackgroundWorker(BackgroundWorker *worker);
 /* Register a new bgworker from a regular backend */
 extern bool RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
 								BackgroundWorkerHandle **handle);
+extern bool RegisterDynamicBackgroundWorkerInternal(BackgroundWorker *worker,
+								BackgroundWorkerHandle **handle,
+								bool parallel);
 
 /* Query the status of a bgworker */
 extern BgwHandleStatus GetBackgroundWorkerPid(BackgroundWorkerHandle *handle,