stat-reset-global-v3.patch

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 1f70fd4..b630bc8 100644
*** a/doc/src/sgml/monitoring.sgml
--- b/doc/src/sgml/monitoring.sgml
*************** postgres: <replaceable>user</> <replacea
*** 918,923 ****
--- 918,934 ----
         (requires superuser privileges)
        </entry>
       </row>
+ 
+      <row>
+       <entry><literal><function>pg_stat_reset_shared</function>()</literal></entry>
+       <entry><type>text</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>
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 4fd2abf..7335a50 100644
*** a/src/backend/postmaster/pgstat.c
--- b/src/backend/postmaster/pgstat.c
*************** static void pgstat_recv_tabstat(PgStat_M
*** 270,275 ****
--- 270,276 ----
  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);
*************** pgstat_reset_counters(void)
*** 1153,1158 ****
--- 1154,1190 ----
  	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")));
+ 		}
+ 
+ 	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSHAREDCOUNTER);
+ 	pgstat_send(&msg, sizeof(msg));
+ }
  
  /* ----------
   * pgstat_report_autovac() -
*************** PgstatCollectorMain(int argc, char *argv
*** 2915,2920 ****
--- 2947,2958 ----
  											 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;
*************** pgstat_recv_resetcounter(PgStat_MsgReset
*** 3869,3874 ****
--- 3907,3930 ----
  }
  
  /* ----------
+  * 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() -
   *
   *	Process an autovacuum signalling message.
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index ab741ca..e5bc95a 100644
*** a/src/backend/utils/adt/pgstatfuncs.c
--- b/src/backend/utils/adt/pgstatfuncs.c
*************** extern Datum pg_stat_get_buf_alloc(PG_FU
*** 78,83 ****
--- 78,84 ----
  
  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;
*************** pg_stat_reset(PG_FUNCTION_ARGS)
*** 1108,1110 ****
--- 1109,1123 ----
  
  	PG_RETURN_VOID();
  }
+ 
+ /* Reset some shared cluster-wide counters */
+ Datum
+ pg_stat_reset_shared(PG_FUNCTION_ARGS)
+ {
+ 	char	*target;
+     target = TextDatumGetCString(PG_GETARG_DATUM(0));
+ 
+ 	pgstat_reset_shared_counters(target);
+ 
+ 	PG_RETURN_VOID();
+ }
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index a8efed9..87072fc 100644
*** a/src/include/catalog/pg_proc.h
--- b/src/include/catalog/pg_proc.h
*************** DATA(insert OID = 2230 (  pg_stat_clear_
*** 3071,3076 ****
--- 3071,3078 ----
  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");
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 3cc334c..c3de665 100644
*** a/src/include/pgstat.h
--- b/src/include/pgstat.h
*************** typedef enum StatMsgType
*** 38,43 ****
--- 38,44 ----
  	PGSTAT_MTYPE_TABPURGE,
  	PGSTAT_MTYPE_DROPDB,
  	PGSTAT_MTYPE_RESETCOUNTER,
+ 	PGSTAT_MTYPE_RESETSHAREDCOUNTER,
  	PGSTAT_MTYPE_AUTOVAC_START,
  	PGSTAT_MTYPE_VACUUM,
  	PGSTAT_MTYPE_ANALYZE,
*************** typedef struct PgStat_TableCounts
*** 93,98 ****
--- 94,105 ----
  	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
*************** typedef struct PgStat_MsgResetcounter
*** 260,265 ****
--- 267,282 ----
  	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
*************** typedef union PgStat_Msg
*** 414,419 ****
--- 431,437 ----
  	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;
*************** extern void pgstat_drop_database(Oid dat
*** 635,640 ****
--- 653,659 ----
  
  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,