Added GUC variable bgwriter_flush_method controlling the action

done by the background writer between writing dirty blocks and
napping.

    none (default)   no action
	sync             bgwriter calls smgrsync() causing a sync(2)

A global sync() is only good on dedicated database servers, so
more flush methods should be added in the future.

Jan

src/backend/utils/misc/guc.c

@@ -10,7 +10,7 @@
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.179 2004/01/23 23:54:21 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.180 2004/01/24 20:00:45 wieck Exp $
  *
  *--------------------------------------------------------------------
  */
@@ -95,6 +95,8 @@ static const char *assign_msglvl(int *var, const char *newval,
 static const char *assign_log_error_verbosity(const char *newval, bool doit,
 						   GucSource source);
 static bool assign_phony_autocommit(bool newval, bool doit, GucSource source);
+extern const char *BgWriterAssignSyncMethod(const char *method,
+						   bool doit, GucSource source);
 
 
 /*
@@ -1689,6 +1691,15 @@ static struct config_string ConfigureNamesString[] =
 		XLOG_sync_method_default, assign_xlog_sync_method, NULL
 	},
 
+	{
+		{"bgwriter_flush_method", PGC_SIGHUP, RESOURCES,
+			gettext_noop("Selects the method used by the bgwriter for forcing writes out to disk."),
+			NULL
+		},
+		&BgWriterFlushMethod_str,
+		BgWriterFlushMethod_default, BgWriterAssignSyncMethod, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, NULL, NULL, NULL

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

@@ -61,9 +61,12 @@
 #debug_shared_buffers = 0	# 0-600 seconds
 
 # - Background writer -
+#debug_shared_buffers = 0	# 0-600 seconds interval (0 = off)
 #bgwriter_delay = 200		# 10-5000 milliseconds
 #bgwriter_percent = 1		# 0-100% of dirty buffers
 #bgwriter_maxpages = 100	# 1-1000 buffers max at once
+#bgwriter_flush_method = none # how the bgwriter flushes kernel buffers
+							# one of: none or sync
 
 # - Free Space Map -