Reduce the default for max_worker_processes back to 8.

Commit b460f5d669 -- at my suggestion --
increased the default value of max_worker_processes from 8 to 16, on
the theory that this would be harmless and convenient for users.
Unfortunately, this caused some buildfarm machines with low connection
limits to start failing, so apparently it's not harmless after all.

doc/src/sgml/config.sgml

@@ -1982,7 +1982,7 @@ include_dir 'conf.d'
         <para>
          Sets the maximum number of background processes that the system
          can support.  This parameter can only be set at server start.  The
-         default is 16.
+         default is 8.
         </para>
 
         <para>

src/backend/utils/init/globals.c

@@ -121,7 +121,7 @@ int			replacement_sort_tuples = 150000;
  */
 int			NBuffers = 1000;
 int			MaxConnections = 90;
-int			max_worker_processes = 16;
+int			max_worker_processes = 8;
 int			max_parallel_workers = 8;
 int			MaxBackends = 0;
 

src/backend/utils/misc/guc.c

@@ -2477,7 +2477,7 @@ static struct config_int ConfigureNamesInt[] =
 			NULL,
 		},
 		&max_worker_processes,
-		16, 0, MAX_BACKENDS,
+		8, 0, MAX_BACKENDS,
 		check_max_worker_processes, NULL, NULL
 	},
 

src/backend/utils/misc/postgresql.conf.sample

@@ -161,7 +161,7 @@
 # - Asynchronous Behavior -
 
 #effective_io_concurrency = 1		# 1-1000; 0 disables prefetching
-#max_worker_processes = 16		# (change requires restart)
+#max_worker_processes = 8		# (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

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 = 16;
+	ControlFile.max_worker_processes = 8;
 	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 = 16;
+	ControlFile.max_worker_processes = 8;
 	ControlFile.max_prepared_xacts = 0;
 	ControlFile.max_locks_per_xact = 64;