Refactor some code related to transaction-level statistics for relations

michaelpq · michaelpq · commit bf01e1ba963a · 2023-10-30T08:23:39.000+09:00
This commit refactors find_tabstat_entry() so as transaction counters for inserted, updated and deleted tuples are included in the result returned. If a shared entry is found for a relation, its result is now a copy of the PgStat_TableStatus entry retrieved from shared memory. This idea has been proposed by Andres Freund. While on it, the following SQL functions, used in system views, are refactored with macros, in the same spirit as 83a1a1b, reducing the amount of code: - pg_stat_get_xact_tuples_deleted() - pg_stat_get_xact_tuples_inserted() - pg_stat_get_xact_tuples_updated() There is now only one caller of find_tabstat_entry() in the tree. Author: Bertrand Drouvot Discussion: https://postgr.es/m/b9e1f543-ee93-8168-d530-d961708ad9d3@gmail.com
diff --git a/src/backend/utils/activity/pgstat_relation.c b/src/backend/utils/activity/pgstat_relation.c
@@ -478,20 +478,52 @@ pgstat_fetch_stat_tabentry_ext(bool shared, Oid reloid)
  * Find any existing PgStat_TableStatus entry for rel_id in the current
  * database. If not found, try finding from shared tables.
  *
- * If no entry found, return NULL, don't create a new one
+ * If an entry is found, copy it and increment the copy's counters with their
+ * subtransaction counterparts, then return the copy.  The caller may need to
+ * pfree() the copy.
+ *
+ * If no entry found, return NULL, don't create a new one.
  */
 PgStat_TableStatus *
 find_tabstat_entry(Oid rel_id)
 {
 	PgStat_EntryRef *entry_ref;
+	PgStat_TableXactStatus *trans;
+	PgStat_TableStatus *tabentry = NULL;
+	PgStat_TableStatus *tablestatus = NULL;
 
 	entry_ref = pgstat_fetch_pending_entry(PGSTAT_KIND_RELATION, MyDatabaseId, rel_id);
 	if (!entry_ref)
+	{
 		entry_ref = pgstat_fetch_pending_entry(PGSTAT_KIND_RELATION, InvalidOid, rel_id);
+		if (!entry_ref)
+			return tablestatus;
+	}
+
+	tabentry = (PgStat_TableStatus *) entry_ref->pending;
+	tablestatus = palloc(sizeof(PgStat_TableStatus));
+	*tablestatus = *tabentry;
+
+	/*
+	 * Reset tablestatus->trans in the copy of PgStat_TableStatus as it may
+	 * point to a shared memory area.  Its data is saved below, so removing it
+	 * does not matter.
+	 */
+	tablestatus->trans = NULL;
+
+	/*
+	 * Live subtransaction counts are not included yet.  This is not a hot
+	 * code path so reconcile tuples_inserted, tuples_updated and
+	 * tuples_deleted even if the caller may not be interested in this data.
+	 */
+	for (trans = tabentry->trans; trans != NULL; trans = trans->upper)
+	{
+		tablestatus->counts.tuples_inserted += trans->tuples_inserted;
+		tablestatus->counts.tuples_updated += trans->tuples_updated;
+		tablestatus->counts.tuples_deleted += trans->tuples_deleted;
+	}
 
-	if (entry_ref)
-		return entry_ref->pending;
-	return NULL;
+	return tablestatus;
 }
 
 /*
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
@@ -1588,68 +1588,14 @@ PG_STAT_GET_XACT_RELENTRY_INT64(blocks_fetched)
 /* pg_stat_get_xact_blocks_hit */
 PG_STAT_GET_XACT_RELENTRY_INT64(blocks_hit)
 
-Datum
-pg_stat_get_xact_tuples_inserted(PG_FUNCTION_ARGS)
-{
-	Oid			relid = PG_GETARG_OID(0);
-	int64		result;
-	PgStat_TableStatus *tabentry;
-	PgStat_TableXactStatus *trans;
+/* pg_stat_get_xact_tuples_inserted */
+PG_STAT_GET_XACT_RELENTRY_INT64(tuples_inserted)
 
-	if ((tabentry = find_tabstat_entry(relid)) == NULL)
-		result = 0;
-	else
-	{
-		result = tabentry->counts.tuples_inserted;
-		/* live subtransactions' counts aren't in tuples_inserted yet */
-		for (trans = tabentry->trans; trans != NULL; trans = trans->upper)
-			result += trans->tuples_inserted;
-	}
+/* pg_stat_get_xact_tuples_updated */
+PG_STAT_GET_XACT_RELENTRY_INT64(tuples_updated)
 
-	PG_RETURN_INT64(result);
-}
-
-Datum
-pg_stat_get_xact_tuples_updated(PG_FUNCTION_ARGS)
-{
-	Oid			relid = PG_GETARG_OID(0);
-	int64		result;
-	PgStat_TableStatus *tabentry;
-	PgStat_TableXactStatus *trans;
-
-	if ((tabentry = find_tabstat_entry(relid)) == NULL)
-		result = 0;
-	else
-	{
-		result = tabentry->counts.tuples_updated;
-		/* live subtransactions' counts aren't in tuples_updated yet */
-		for (trans = tabentry->trans; trans != NULL; trans = trans->upper)
-			result += trans->tuples_updated;
-	}
-
-	PG_RETURN_INT64(result);
-}
-
-Datum
-pg_stat_get_xact_tuples_deleted(PG_FUNCTION_ARGS)
-{
-	Oid			relid = PG_GETARG_OID(0);
-	int64		result;
-	PgStat_TableStatus *tabentry;
-	PgStat_TableXactStatus *trans;
-
-	if ((tabentry = find_tabstat_entry(relid)) == NULL)
-		result = 0;
-	else
-	{
-		result = tabentry->counts.tuples_deleted;
-		/* live subtransactions' counts aren't in tuples_deleted yet */
-		for (trans = tabentry->trans; trans != NULL; trans = trans->upper)
-			result += trans->tuples_deleted;
-	}
-
-	PG_RETURN_INT64(result);
-}
+/* pg_stat_get_xact_tuples_deleted */
+PG_STAT_GET_XACT_RELENTRY_INT64(tuples_deleted)
 
 Datum
 pg_stat_get_xact_function_calls(PG_FUNCTION_ARGS)
