From: Chao Li <li.evan.chao@gmail.com>
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Subject: Fix pgstat_database.c to honor passed database OIDs
Message-Id: <ABBD5026-506F-4006-A569-28F72C188693@gmail.com>
Date: Fri, 10 Apr 2026 13:53:15 +0800
To: PostgreSQL-development <pgsql-hackers@postgresql.org>
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Hi,

In pgstat_database.c, pgstat_report_connect(), =
pgstat_report_disconnect(), and pgstat_reset_database_timestamp() all =
take a dboid parameter, but currently ignore it and use MyDatabaseId =
instead. While that does not seem to break anything today, it at least =
hurts readability.

This patch changes those three functions to use the passed dboid.

For pgstat_report_connect() and pgstat_report_disconnect(), there is =
only one caller, and it passes MyDatabaseId, so this change should be =
safe.

For pgstat_reset_database_timestamp(), in most paths dboid is also just =
MyDatabaseId. However, there is one path where dboid can be InvalidOid:

1 - pg_stat_reset_single_table_counters may pass InvalidOid to =
pgstat_reset for a shared relation.
```
Datum
pg_stat_reset_single_table_counters(PG_FUNCTION_ARGS)
{
	Oid			taboid =3D PG_GETARG_OID(0);
	Oid			dboid =3D (IsSharedRelation(taboid) ? =
InvalidOid : MyDatabaseId);

	pgstat_reset(PGSTAT_KIND_RELATION, dboid, taboid);

	PG_RETURN_VOID();
}
```

2 - pgstat_reset only calls pgstat_reset_database_timestamp when =
kind_info->accessed_across_databases is false.
```
void
pgstat_reset(PgStat_Kind kind, Oid dboid, uint64 objid)
{
	const PgStat_KindInfo *kind_info =3D pgstat_get_kind_info(kind);
	TimestampTz ts =3D GetCurrentTimestamp();

	/* not needed atm, and doesn't make sense with the current =
signature */
	Assert(!pgstat_get_kind_info(kind)->fixed_amount);

	/* reset the "single counter" */
	pgstat_reset_entry(kind, dboid, objid, ts);

	if (!kind_info->accessed_across_databases)
		pgstat_reset_database_timestamp(dboid, ts);
}
```

3 - In this path, kind is PGSTAT_KIND_RELATION, and =
accessed_across_databases is false:
```
	[PGSTAT_KIND_RELATION] =3D {
		.name =3D "relation",

		.fixed_amount =3D false,
		.write_to_file =3D true,

		.shared_size =3D sizeof(PgStatShared_Relation),
		.shared_data_off =3D offsetof(PgStatShared_Relation, =
stats),
		.shared_data_len =3D sizeof(((PgStatShared_Relation *) =
0)->stats),
		.pending_size =3D sizeof(PgStat_TableStatus),

		.flush_pending_cb =3D pgstat_relation_flush_cb,
		.delete_pending_cb =3D =
pgstat_relation_delete_pending_cb,
		.reset_timestamp_cb =3D =
pgstat_relation_reset_timestamp_cb,
	},
```

So in this case, pgstat_reset_database_timestamp() can receive =
InvalidOid as dboid. In the current code, because that function ignores =
dboid and uses MyDatabaseId, calling =
pg_stat_reset_single_table_counters() on a shared relation can =
incorrectly reset the current database's stat_reset_timestamp. That =
behavior seems unintended, so this patch makes =
pgstat_reset_database_timestamp() return immediately when dboid is =
InvalidOid.

Please see the attached patch. =E2=80=9CMake check-world=E2=80=9D passed =
from my side.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/


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=46rom=208e965bb55562a675d17e37de8b20fe17fe4ec452=20Mon=20Sep=2017=20=
00:00:00=202001=0AFrom:=20"Chao=20Li=20(Evan)"=20<lic@highgo.com>=0A=
Date:=20Fri,=2010=20Apr=202026=2011:21:20=20+0800=0ASubject:=20[PATCH=20=
v1]=20Fix=20pgstat_database.c=20to=20honor=20passed=20database=20OIDs=0A=0A=
Several=20functions=20in=20pgstat_database.c=20take=20a=20database=20OID=20=
argument=0Abut=20then=20ignore=20it=20and=20use=20MyDatabaseId=20=
instead.=20That=20is=20confusing,=0Aand=20in=20=
pgstat_reset_database_timestamp()=20it=20is=20plainly=20wrong,=20because=0A=
the=20function's=20contract=20is=20to=20reset=20the=20timestamp=20for=20=
the=20specified=0Adatabase.=0A=0AUse=20the=20passed=20dboid=20in=20=
pgstat_report_connect(),=0Apgstat_report_disconnect(),=20and=20=
pgstat_reset_database_timestamp().=0A=0AAlso=20make=20=
pgstat_reset_database_timestamp()=20return=20immediately=20when=0Acalled=20=
with=20an=20invalid=20OID,=20avoiding=20an=20unnecessary=20stats=20=
lookup.=0A=0AAuthor:=20Chao=20Li=20<lic@highgo.com>=0AReviewed-by:=0A=
Discussion:=20https://postgr.es/m/=0A---=0A=20=
src/backend/utils/activity/pgstat_database.c=20|=209=20++++++---=0A=201=20=
file=20changed,=206=20insertions(+),=203=20deletions(-)=0A=0Adiff=20=
--git=20a/src/backend/utils/activity/pgstat_database.c=20=
b/src/backend/utils/activity/pgstat_database.c=0Aindex=20=
f1846d3236c..36a84d1f0a4=20100644=0A---=20=
a/src/backend/utils/activity/pgstat_database.c=0A+++=20=
b/src/backend/utils/activity/pgstat_database.c=0A@@=20-243,7=20+243,7=20=
@@=20pgstat_report_connect(Oid=20dboid)=0A=20=0A=20=09=
pgLastSessionReportTime=20=3D=20MyStartTimestamp;=0A=20=0A-=09dbentry=20=
=3D=20pgstat_prep_database_pending(MyDatabaseId);=0A+=09dbentry=20=3D=20=
pgstat_prep_database_pending(dboid);=0A=20=09dbentry->sessions++;=0A=20}=0A=
=20=0A@@=20-258,7=20+258,7=20@@=20pgstat_report_disconnect(Oid=20dboid)=0A=
=20=09if=20(!pgstat_should_report_connstat())=0A=20=09=09return;=0A=20=0A=
-=09dbentry=20=3D=20pgstat_prep_database_pending(MyDatabaseId);=0A+=09=
dbentry=20=3D=20pgstat_prep_database_pending(dboid);=0A=20=0A=20=09=
switch=20(pgStatSessionEndCause)=0A=20=09{=0A@@=20-419,7=20+419,10=20@@=20=
pgstat_reset_database_timestamp(Oid=20dboid,=20TimestampTz=20ts)=0A=20=09=
PgStat_EntryRef=20*dbref;=0A=20=09PgStatShared_Database=20*dbentry;=0A=20=
=0A-=09dbref=20=3D=20pgstat_get_entry_ref_locked(PGSTAT_KIND_DATABASE,=20=
MyDatabaseId,=20InvalidOid,=0A+=09if=20(!OidIsValid(dboid))=0A+=09=09=
return;=0A+=0A+=09dbref=20=3D=20=
pgstat_get_entry_ref_locked(PGSTAT_KIND_DATABASE,=20dboid,=20InvalidOid,=0A=
=20=09=09=09=09=09=09=09=09=09=09false);=0A=20=0A=20=09dbentry=20=3D=20=
(PgStatShared_Database=20*)=20dbref->shared_stats;=0A--=20=0A2.50.1=20=
(Apple=20Git-155)=0A=0A=

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