pgstat: add pg_stat_have_stats() test helper.

Will be used by tests committed subsequently.

Bumps catversion (this time for real, the one in 0f96965c65 got lost when
rebasing over 5c279a6d35).

Author: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://postgr.es/m/CAAKRu_aNxL1WegCa45r=VAViCLnpOU7uNC7bTtGw+=QAPyYivw@mail.gmail.com

src/backend/catalog/system_functions.sql

@@ -637,6 +637,8 @@ REVOKE EXECUTE ON FUNCTION pg_stat_reset_single_function_counters(oid) FROM publ
 
 REVOKE EXECUTE ON FUNCTION pg_stat_reset_replication_slot(text) FROM public;
 
+REVOKE EXECUTE ON FUNCTION pg_stat_have_stats(text, oid, oid) FROM public;
+
 REVOKE EXECUTE ON FUNCTION pg_stat_reset_subscription_stats(oid) FROM public;
 
 REVOKE EXECUTE ON FUNCTION lo_import(text) FROM public;

src/backend/utils/activity/pgstat.c

@@ -872,6 +872,16 @@ pgstat_get_stat_snapshot_timestamp(bool *have_snapshot)
 	return 0;
 }
 
+bool
+pgstat_have_entry(PgStat_Kind kind, Oid dboid, Oid objoid)
+{
+	/* fixed-numbered stats always exist */
+	if (pgstat_get_kind_info(kind)->fixed_amount)
+		return true;
+
+	return pgstat_get_entry_ref(kind, dboid, objoid, false, NULL) != NULL;
+}
+
 /*
  * Ensure snapshot for fixed-numbered 'kind' exists.
  *

src/backend/utils/adt/pgstatfuncs.c

@@ -2394,3 +2394,21 @@ pg_stat_get_subscription_stats(PG_FUNCTION_ARGS)
 	/* Returns the record as Datum */
 	PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
 }
+
+/*
+ * Checks for presence of stats for object with provided kind, database oid,
+ * object oid.
+ *
+ * This is useful for tests, but not really anything else. Therefore not
+ * documented.
+ */
+Datum
+pg_stat_have_stats(PG_FUNCTION_ARGS)
+{
+	char	   *stats_type = text_to_cstring(PG_GETARG_TEXT_P(0));
+	Oid			dboid = PG_GETARG_OID(1);
+	Oid			objoid = PG_GETARG_OID(2);
+	PgStat_Kind	kind = pgstat_get_kind_from_str(stats_type);
+
+	PG_RETURN_BOOL(pgstat_have_entry(kind, dboid, objoid));
+}

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202204072
+#define CATALOG_VERSION_NO	202204073
 
 #endif

src/include/catalog/pg_proc.dat

@@ -5376,6 +5376,12 @@
   proargmodes => '{i,o,o,o,o,o,o,o,o,o,o}',
   proargnames => '{slot_name,slot_name,spill_txns,spill_count,spill_bytes,stream_txns,stream_count,stream_bytes,total_txns,total_bytes,stats_reset}',
   prosrc => 'pg_stat_get_replication_slot' },
+
+{ oid => '8384', descr => 'statistics: check if a stats object exists',
+  proname => 'pg_stat_have_stats', provolatile => 'v', proparallel => 'r',
+  prorettype => 'bool', proargtypes => 'text oid oid',
+  prosrc => 'pg_stat_have_stats' },
+
 { oid => '8523', descr => 'statistics: information about subscription stats',
   proname => 'pg_stat_get_subscription_stats',
   provolatile => 's', proparallel => 'r',

src/include/pgstat.h

@@ -426,6 +426,8 @@ extern TimestampTz pgstat_get_stat_snapshot_timestamp(bool *have_snapshot);
 
 /* helpers */
 extern PgStat_Kind pgstat_get_kind_from_str(char *kind_str);
+extern bool pgstat_have_entry(PgStat_Kind kind, Oid dboid, Oid objoid);
+
 
 /*
  * Functions in pgstat_archiver.c