Add stats_reset to pg_stat_user_functions

It is possible to call pg_stat_reset_single_function_counters() for a
single function, but the reset time was missing the system view showing
its statistics.  Like all the fields of pg_stat_user_functions, the GUC
track_functions needs to be enabled to show the statistics about
function executions.

Bump catalog version.
Bump PGSTAT_FILE_FORMAT_ID, as a result of the new field added to
PgStat_StatFuncEntry.

Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Discussion: https://postgr.es/m/aONjnsaJSx-nEdfU@paquier.xyz

doc/src/sgml/monitoring.sgml

@@ -4736,6 +4736,15 @@ description | Waiting for a newly initialized WAL file to reach durable storage
        other functions called by it, in milliseconds
       </para></entry>
      </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+        <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
+       </para>
+       <para>
+        Time at which these statistics were last reset
+       </para></entry>
+     </row>
     </tbody>
    </tgroup>
   </table>

src/backend/catalog/system_views.sql

@@ -1131,7 +1131,8 @@ CREATE VIEW pg_stat_user_functions AS
             P.proname AS funcname,
             pg_stat_get_function_calls(P.oid) AS calls,
             pg_stat_get_function_total_time(P.oid) AS total_time,
-            pg_stat_get_function_self_time(P.oid) AS self_time
+            pg_stat_get_function_self_time(P.oid) AS self_time,
+            pg_stat_get_function_stat_reset_time(P.oid) AS stats_reset
     FROM pg_proc P LEFT JOIN pg_namespace N ON (N.oid = P.pronamespace)
     WHERE P.prolang != 12  -- fast check to eliminate built-in functions
           AND pg_stat_get_function_calls(P.oid) IS NOT NULL;

src/backend/utils/activity/pgstat.c

@@ -328,6 +328,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE]
 		.pending_size = sizeof(PgStat_FunctionCounts),
 
 		.flush_pending_cb = pgstat_function_flush_cb,
+		.reset_timestamp_cb = pgstat_function_reset_timestamp_cb,
 	},
 
 	[PGSTAT_KIND_REPLSLOT] = {

src/backend/utils/activity/pgstat_function.c

@@ -214,6 +214,12 @@ pgstat_function_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 	return true;
 }
 
+void
+pgstat_function_reset_timestamp_cb(PgStatShared_Common *header, TimestampTz ts)
+{
+	((PgStatShared_Function *) header)->stats.stat_reset_timestamp = ts;
+}
+
 /*
  * find any existing PgStat_FunctionCounts entry for specified function
  *

src/backend/utils/adt/pgstatfuncs.c

@@ -203,6 +203,24 @@ PG_STAT_GET_FUNCENTRY_FLOAT8_MS(total_time)
 /* pg_stat_get_function_self_time */
 PG_STAT_GET_FUNCENTRY_FLOAT8_MS(self_time)
 
+Datum
+pg_stat_get_function_stat_reset_time(PG_FUNCTION_ARGS)
+{
+	Oid			funcid = PG_GETARG_OID(0);
+	TimestampTz result;
+	PgStat_StatFuncEntry *funcentry;
+
+	if ((funcentry = pgstat_fetch_stat_funcentry(funcid)) == NULL)
+		result = 0;
+	else
+		result = funcentry->stat_reset_timestamp;
+
+	if (result == 0)
+		PG_RETURN_NULL();
+	else
+		PG_RETURN_TIMESTAMPTZ(result);
+}
+
 Datum
 pg_stat_get_backend_idset(PG_FUNCTION_ARGS)
 {

src/include/catalog/catversion.h

@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202510062
+#define CATALOG_VERSION_NO	202510081
 
 #endif

src/include/catalog/pg_proc.dat

@@ -6071,6 +6071,10 @@
   proname => 'pg_stat_get_function_self_time', provolatile => 's',
   proparallel => 'r', prorettype => 'float8', proargtypes => 'oid',
   prosrc => 'pg_stat_get_function_self_time' },
+{ oid => '8745', descr => 'statistics: last reset for a function',
+  proname => 'pg_stat_get_function_stat_reset_time', provolatile => 's',
+  proparallel => 'r', prorettype => 'timestamptz', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_function_stat_reset_time' },
 
 { oid => '3037',
   descr => 'statistics: number of scans done for table/index in current transaction',

src/include/pgstat.h

@@ -212,7 +212,7 @@ typedef struct PgStat_TableXactStatus
  * ------------------------------------------------------------
  */
 
-#define PGSTAT_FILE_FORMAT_ID	0x01A5BCB8
+#define PGSTAT_FILE_FORMAT_ID	0x01A5BCB9
 
 typedef struct PgStat_ArchiverStats
 {
@@ -384,6 +384,7 @@ typedef struct PgStat_StatFuncEntry
 
 	PgStat_Counter total_time;	/* times in microseconds */
 	PgStat_Counter self_time;
+	TimestampTz stat_reset_timestamp;
 } PgStat_StatFuncEntry;
 
 typedef struct PgStat_StatReplSlotEntry

src/include/utils/pgstat_internal.h

@@ -691,6 +691,7 @@ extern void pgstat_database_reset_timestamp_cb(PgStatShared_Common *header, Time
  */
 
 extern bool pgstat_function_flush_cb(PgStat_EntryRef *entry_ref, bool nowait);
+extern void pgstat_function_reset_timestamp_cb(PgStatShared_Common *header, TimestampTz ts);
 
 
 /*

src/test/isolation/expected/stats.out

@@ -1025,7 +1025,7 @@ test_stat_func|                          |                |
 (1 row)
 
 
-starting permutation: s1_track_funcs_all s2_track_funcs_all s1_func_call s2_func_call s2_func_call2 s1_ff s2_ff s1_func_stats s2_func_call s2_func_call2 s2_ff s1_func_stats s1_func_stats2 s1_func_stats s1_func_stats_reset s1_func_stats s1_func_stats2 s1_func_stats
+starting permutation: s1_track_funcs_all s2_track_funcs_all s1_func_call s2_func_call s2_func_call2 s1_ff s2_ff s1_func_stats s2_func_call s2_func_call2 s2_ff s1_func_stats s1_func_stats2 s1_func_stats s1_func_stats_reset_check s1_func_stats_reset s1_func_stats s1_func_stats2 s1_func_stats s1_func_stats_reset_check
 pg_stat_force_next_flush
 ------------------------
                         
@@ -1137,6 +1137,15 @@ name          |pg_stat_get_function_calls|total_above_zero|self_above_zero
 test_stat_func|                         3|t               |t              
 (1 row)
 
+step s1_func_stats_reset_check: 
+    SELECT pg_stat_get_function_stat_reset_time('test_stat_func'::regproc)
+        IS NOT NULL AS has_stats_reset;
+
+has_stats_reset
+---------------
+f              
+(1 row)
+
 step s1_func_stats_reset: SELECT pg_stat_reset_single_function_counters('test_stat_func'::regproc);
 pg_stat_reset_single_function_counters
 --------------------------------------
@@ -1185,6 +1194,15 @@ name          |pg_stat_get_function_calls|total_above_zero|self_above_zero
 test_stat_func|                         0|f               |f              
 (1 row)
 
+step s1_func_stats_reset_check: 
+    SELECT pg_stat_get_function_stat_reset_time('test_stat_func'::regproc)
+        IS NOT NULL AS has_stats_reset;
+
+has_stats_reset
+---------------
+t              
+(1 row)
+
 
 starting permutation: s1_func_stats_nonexistent s1_func_stats_reset_nonexistent s1_func_stats_nonexistent
 pg_stat_force_next_flush

src/test/isolation/expected/stats_1.out

@@ -1025,7 +1025,7 @@ test_stat_func|                          |                |
 (1 row)
 
 
-starting permutation: s1_track_funcs_all s2_track_funcs_all s1_func_call s2_func_call s2_func_call2 s1_ff s2_ff s1_func_stats s2_func_call s2_func_call2 s2_ff s1_func_stats s1_func_stats2 s1_func_stats s1_func_stats_reset s1_func_stats s1_func_stats2 s1_func_stats
+starting permutation: s1_track_funcs_all s2_track_funcs_all s1_func_call s2_func_call s2_func_call2 s1_ff s2_ff s1_func_stats s2_func_call s2_func_call2 s2_ff s1_func_stats s1_func_stats2 s1_func_stats s1_func_stats_reset_check s1_func_stats_reset s1_func_stats s1_func_stats2 s1_func_stats s1_func_stats_reset_check
 pg_stat_force_next_flush
 ------------------------
                         
@@ -1137,6 +1137,15 @@ name          |pg_stat_get_function_calls|total_above_zero|self_above_zero
 test_stat_func|                         3|t               |t              
 (1 row)
 
+step s1_func_stats_reset_check: 
+    SELECT pg_stat_get_function_stat_reset_time('test_stat_func'::regproc)
+        IS NOT NULL AS has_stats_reset;
+
+has_stats_reset
+---------------
+f              
+(1 row)
+
 step s1_func_stats_reset: SELECT pg_stat_reset_single_function_counters('test_stat_func'::regproc);
 pg_stat_reset_single_function_counters
 --------------------------------------
@@ -1185,6 +1194,15 @@ name          |pg_stat_get_function_calls|total_above_zero|self_above_zero
 test_stat_func|                         0|f               |f              
 (1 row)
 
+step s1_func_stats_reset_check: 
+    SELECT pg_stat_get_function_stat_reset_time('test_stat_func'::regproc)
+        IS NOT NULL AS has_stats_reset;
+
+has_stats_reset
+---------------
+t              
+(1 row)
+
 
 starting permutation: s1_func_stats_nonexistent s1_func_stats_reset_nonexistent s1_func_stats_nonexistent
 pg_stat_force_next_flush

src/test/isolation/specs/stats.spec

@@ -58,6 +58,10 @@ step s1_track_funcs_none { SET track_functions = 'none'; }
 step s1_func_call { SELECT test_stat_func(); }
 step s1_func_drop { DROP FUNCTION test_stat_func(); }
 step s1_func_stats_reset { SELECT pg_stat_reset_single_function_counters('test_stat_func'::regproc); }
+step s1_func_stats_reset_check {
+    SELECT pg_stat_get_function_stat_reset_time('test_stat_func'::regproc)
+        IS NOT NULL AS has_stats_reset;
+}
 step s1_func_stats_reset_nonexistent { SELECT pg_stat_reset_single_function_counters(12000); }
 step s1_reset { SELECT pg_stat_reset(); }
 step s1_func_stats {
@@ -235,9 +239,9 @@ permutation
   s1_ff s2_ff
   s1_func_stats
   s2_func_call s2_func_call2 s2_ff
-  s1_func_stats s1_func_stats2 s1_func_stats
+  s1_func_stats s1_func_stats2 s1_func_stats s1_func_stats_reset_check
   s1_func_stats_reset
-  s1_func_stats s1_func_stats2 s1_func_stats
+  s1_func_stats s1_func_stats2 s1_func_stats s1_func_stats_reset_check
 
 # test pg_stat_reset_single_function_counters of non-existing function
 permutation

src/test/regress/expected/rules.out

@@ -2244,7 +2244,8 @@ pg_stat_user_functions| SELECT p.oid AS funcid,
     p.proname AS funcname,
     pg_stat_get_function_calls(p.oid) AS calls,
     pg_stat_get_function_total_time(p.oid) AS total_time,
-    pg_stat_get_function_self_time(p.oid) AS self_time
+    pg_stat_get_function_self_time(p.oid) AS self_time,
+    pg_stat_get_function_stat_reset_time(p.oid) AS stats_reset
    FROM (pg_proc p
      LEFT JOIN pg_namespace n ON ((n.oid = p.pronamespace)))
   WHERE ((p.prolang <> (12)::oid) AND (pg_stat_get_function_calls(p.oid) IS NOT NULL));