From: Michael Paquier <michael@paquier.xyz>
Date: Wed, 1 Jul 2026 03:17:17 +0000 (+0900)
Subject: Avoid useless calls in pg_get_multixact_stats()
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=b542d556670586ebadf380102f6ead920609e592;p=thirdparty%2Fpostgresql.git

Avoid useless calls in pg_get_multixact_stats()

MultiXactOffsetStorageSize() and GetMultiXactInfo() are called to gather
the information reported by the function, but were wasteful for the case
where a role does not have the privileges of pg_read_all_stats, where we
return a set of NULLs.  These calls are moved to the code path where
their results are used.

Author: Ranier Vilela <ranier.vf@gmail.com>
Discussion: https://postgr.es/m/CAEudQAonQh7be=wOR-CJFW=bgMBz5wW_bv4t0OFxbgn-794JCQ@mail.gmail.com
Backpatch-through: 19
---

diff --git a/src/backend/utils/adt/multixactfuncs.c b/src/backend/utils/adt/multixactfuncs.c
index 9fe2ebafa73..d9aa58e821d 100644
--- a/src/backend/utils/adt/multixactfuncs.c
+++ b/src/backend/utils/adt/multixactfuncs.c
@@ -102,23 +102,12 @@ pg_get_multixact_stats(PG_FUNCTION_ARGS)
 	TupleDesc	tupdesc;
 	Datum		values[4];
 	bool		nulls[4];
-	uint64		members;
-	MultiXactId oldestMultiXactId;
-	uint32		multixacts;
-	MultiXactOffset oldestOffset;
-	MultiXactOffset nextOffset;
-	uint64		membersBytes;
 
 	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("return type must be a row type")));
 
-	GetMultiXactInfo(&multixacts, &nextOffset, &oldestMultiXactId, &oldestOffset);
-	members = nextOffset - oldestOffset;
-
-	membersBytes = MultiXactOffsetStorageSize(nextOffset, oldestOffset);
-
 	if (!has_privs_of_role(GetUserId(), ROLE_PG_READ_ALL_STATS))
 	{
 		/*
@@ -129,6 +118,17 @@ pg_get_multixact_stats(PG_FUNCTION_ARGS)
 	}
 	else
 	{
+		uint64		members;
+		MultiXactId oldestMultiXactId;
+		uint32		multixacts;
+		MultiXactOffset oldestOffset;
+		MultiXactOffset nextOffset;
+		uint64		membersBytes;
+
+		GetMultiXactInfo(&multixacts, &nextOffset, &oldestMultiXactId, &oldestOffset);
+		members = nextOffset - oldestOffset;
+		membersBytes = MultiXactOffsetStorageSize(nextOffset, oldestOffset);
+
 		values[0] = UInt32GetDatum(multixacts);
 		values[1] = Int64GetDatum(members);
 		values[2] = Int64GetDatum(membersBytes);