Add pg_stat_reset_shared('bgwriter') to reset the cluster-wide shared

statistics of the bgwriter.

Greg Smith

doc/src/sgml/monitoring.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/monitoring.sgml,v 1.73 2009/11/29 18:14:30 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/monitoring.sgml,v 1.74 2010/01/19 14:11:30 mha Exp $ -->
 
 <chapter id="monitoring">
  <title>Monitoring Database Activity</title>
@@ -918,6 +918,17 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
        (requires superuser privileges)
       </entry>
      </row>
+
+     <row>
+      <entry><literal><function>pg_stat_reset_shared</function>(text)</literal></entry>
+      <entry><type>void</type></entry>
+      <entry>
+       Reset some of the shared statistics counters for the database cluster to
+       zero (requires superuser privileges).  Calling
+       <literal>pg_stat_reset_shared('bgwriter')</> will zero all the values shown by
+       <structname>pg_stat_bgwriter</>.
+      </entry>
+     </row>
     </tbody>
    </tgroup>
   </table>

src/backend/postmaster/pgstat.c

@@ -13,7 +13,7 @@
  *
  *	Copyright (c) 2001-2010, PostgreSQL Global Development Group
  *
- *	$PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.197 2010/01/10 14:16:07 mha Exp $
+ *	$PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.198 2010/01/19 14:11:30 mha Exp $
  * ----------
  */
 #include "postgres.h"
@@ -270,6 +270,7 @@ static void pgstat_recv_tabstat(PgStat_MsgTabstat *msg, int len);
 static void pgstat_recv_tabpurge(PgStat_MsgTabpurge *msg, int len);
 static void pgstat_recv_dropdb(PgStat_MsgDropdb *msg, int len);
 static void pgstat_recv_resetcounter(PgStat_MsgResetcounter *msg, int len);
+static void pgstat_recv_resetsharedcounter(PgStat_MsgResetsharedcounter *msg, int len);
 static void pgstat_recv_autovac(PgStat_MsgAutovacStart *msg, int len);
 static void pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len);
 static void pgstat_recv_analyze(PgStat_MsgAnalyze *msg, int len);
@@ -1153,6 +1154,38 @@ pgstat_reset_counters(void)
 	pgstat_send(&msg, sizeof(msg));
 }
 
+/* ----------
+ * pgstat_reset_shared_counters() -
+ *
+ *	Tell the statistics collector to reset cluster-wide shared counters.
+ * ----------
+ */
+void
+pgstat_reset_shared_counters(const char *target)
+{
+	PgStat_MsgResetsharedcounter msg;
+
+	if (pgStatSock < 0)
+		return;
+
+	if (!superuser())
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("must be superuser to reset statistics counters")));
+
+	if (strcmp(target, "bgwriter") == 0)
+		msg.m_resettarget = RESET_BGWRITER;
+	else
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_SYNTAX_ERROR),
+				 errmsg("unrecognized reset target: '%s'", target),
+				 errhint("allowed targets are 'bgwriter'.")));
+	}
+
+	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSHAREDCOUNTER);
+	pgstat_send(&msg, sizeof(msg));
+}
 
 /* ----------
  * pgstat_report_autovac() -
@@ -2915,6 +2948,12 @@ PgstatCollectorMain(int argc, char *argv[])
 											 len);
 					break;
 
+				case PGSTAT_MTYPE_RESETSHAREDCOUNTER:
+					pgstat_recv_resetsharedcounter(
+											 (PgStat_MsgResetsharedcounter *) &msg,
+											 len);
+					break;
+
 				case PGSTAT_MTYPE_AUTOVAC_START:
 					pgstat_recv_autovac((PgStat_MsgAutovacStart *) &msg, len);
 					break;
@@ -3868,6 +3907,27 @@ pgstat_recv_resetcounter(PgStat_MsgResetcounter *msg, int len)
 									 HASH_ELEM | HASH_FUNCTION);
 }
 
+/* ----------
+ * pgstat_recv_resetshared() -
+ *
+ *	Reset some shared statistics of the cluster.
+ * ----------
+ */
+static void
+pgstat_recv_resetsharedcounter(PgStat_MsgResetsharedcounter *msg, int len)
+{
+    if (msg->m_resettarget==RESET_BGWRITER)
+	{
+		/* Reset the global background writer statistics for the cluster. */
+		memset(&globalStats, 0, sizeof(globalStats));
+	}
+
+	/*
+	 * Presumably the sender of this message validated the target, don't
+	 * complain here if it's not valid
+	 */
+}
+
 /* ----------
  * pgstat_recv_autovac() -
  *

src/backend/utils/adt/pgstatfuncs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/pgstatfuncs.c,v 1.57 2010/01/02 16:57:54 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/pgstatfuncs.c,v 1.58 2010/01/19 14:11:31 mha Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -78,6 +78,7 @@ extern Datum pg_stat_get_buf_alloc(PG_FUNCTION_ARGS);
 
 extern Datum pg_stat_clear_snapshot(PG_FUNCTION_ARGS);
 extern Datum pg_stat_reset(PG_FUNCTION_ARGS);
+extern Datum pg_stat_reset_shared(PG_FUNCTION_ARGS);
 
 /* Global bgwriter statistics, from bgwriter.c */
 extern PgStat_MsgBgWriter bgwriterStats;
@@ -1108,3 +1109,14 @@ pg_stat_reset(PG_FUNCTION_ARGS)
 
 	PG_RETURN_VOID();
 }
+
+/* Reset some shared cluster-wide counters */
+Datum
+pg_stat_reset_shared(PG_FUNCTION_ARGS)
+{
+	char	*target = text_to_cstring(PG_GETARG_TEXT_PP(0));
+
+	pgstat_reset_shared_counters(target);
+
+	PG_RETURN_VOID();
+}

src/include/catalog/catversion.h

@@ -37,7 +37,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.575 2010/01/19 05:50:18 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.576 2010/01/19 14:11:32 mha Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201001181
+#define CATALOG_VERSION_NO	201001191
 
 #endif

src/include/catalog/pg_proc.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.563 2010/01/19 05:50:18 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.564 2010/01/19 14:11:32 mha Exp $
  *
  * NOTES
  *	  The script catalog/genbki.pl reads this file and generates .bki
@@ -3073,6 +3073,8 @@ DATA(insert OID = 2230 (  pg_stat_clear_snapshot		PGNSP PGUID 12 1 0 0 f f f f f
 DESCR("statistics: discard current transaction's statistics snapshot");
 DATA(insert OID = 2274 (  pg_stat_reset					PGNSP PGUID 12 1 0 0 f f f f f v 0 0 2278 "" _null_ _null_ _null_ _null_	pg_stat_reset _null_ _null_ _null_ ));
 DESCR("statistics: reset collected statistics for current database");
+DATA(insert OID = 3775 (  pg_stat_reset_shared			PGNSP PGUID 12 1 0 0 f f f f f v 1 0 2278 "25" _null_ _null_ _null_ _null_	pg_stat_reset_shared _null_ _null_ _null_ ));
+DESCR("statistics: reset collected statistics shared across the cluster");
 
 DATA(insert OID = 1946 (  encode						PGNSP PGUID 12 1 0 0 f f f t f i 2 0 25 "17 25" _null_ _null_ _null_ _null_ binary_encode _null_ _null_ _null_ ));
 DESCR("convert bytea value into some ascii-only text string");

src/include/pgstat.h

@@ -5,7 +5,7 @@
  *
  *	Copyright (c) 2001-2010, PostgreSQL Global Development Group
  *
- *	$PostgreSQL: pgsql/src/include/pgstat.h,v 1.86 2010/01/02 16:58:00 momjian Exp $
+ *	$PostgreSQL: pgsql/src/include/pgstat.h,v 1.87 2010/01/19 14:11:31 mha Exp $
  * ----------
  */
 #ifndef PGSTAT_H
@@ -38,6 +38,7 @@ typedef enum StatMsgType
 	PGSTAT_MTYPE_TABPURGE,
 	PGSTAT_MTYPE_DROPDB,
 	PGSTAT_MTYPE_RESETCOUNTER,
+	PGSTAT_MTYPE_RESETSHAREDCOUNTER,
 	PGSTAT_MTYPE_AUTOVAC_START,
 	PGSTAT_MTYPE_VACUUM,
 	PGSTAT_MTYPE_ANALYZE,
@@ -93,6 +94,12 @@ typedef struct PgStat_TableCounts
 	PgStat_Counter t_blocks_hit;
 } PgStat_TableCounts;
 
+/* Possible targets for resetting cluster-wide shared values */
+typedef enum PgStat_Shared_Reset_Target
+{
+    RESET_BGWRITER
+} PgStat_Shared_Reset_Target;
+
 
 /* ------------------------------------------------------------
  * Structures kept in backend local memory while accumulating counts
@@ -260,6 +267,16 @@ typedef struct PgStat_MsgResetcounter
 	Oid			m_databaseid;
 } PgStat_MsgResetcounter;
 
+/* ----------
+ * PgStat_MsgResetsharedcounter	Sent by the backend to tell the collector
+ *								to reset a shared counter
+ * ----------
+ */
+typedef struct PgStat_MsgResetsharedcounter
+{
+	PgStat_MsgHdr m_hdr;
+	PgStat_Shared_Reset_Target m_resettarget;
+} PgStat_MsgResetsharedcounter;
 
 /* ----------
  * PgStat_MsgAutovacStart		Sent by the autovacuum daemon to signal
@@ -414,6 +431,7 @@ typedef union PgStat_Msg
 	PgStat_MsgTabpurge msg_tabpurge;
 	PgStat_MsgDropdb msg_dropdb;
 	PgStat_MsgResetcounter msg_resetcounter;
+	PgStat_MsgResetsharedcounter msg_resetsharedcounter;
 	PgStat_MsgAutovacStart msg_autovacuum;
 	PgStat_MsgVacuum msg_vacuum;
 	PgStat_MsgAnalyze msg_analyze;
@@ -635,6 +653,7 @@ extern void pgstat_drop_database(Oid databaseid);
 
 extern void pgstat_clear_snapshot(void);
 extern void pgstat_reset_counters(void);
+extern void pgstat_reset_shared_counters(const char *);
 
 extern void pgstat_report_autovac(Oid dboid);
 extern void pgstat_report_vacuum(Oid tableoid, bool shared, bool adopt_counts,