Deduplicate code in LargeObjectExists and myLargeObjectExists.

myLargeObjectExists() and LargeObjectExists() had nearly identical code,
except for handling snapshots. This commit renames myLargeObjectExists()
to LargeObjectExistsWithSnapshot() and refactors LargeObjectExists()
to call it internally, reducing duplication.

Author: Yugo Nagata
Reviewed-by: Fujii Masao
Discussion: https://postgr.es/m/20240702163444.ab586f6075e502eb84f11b1a@sranhm.sraoss.co.jp

src/backend/catalog/pg_largeobject.c

@@ -14,8 +14,6 @@
  */
 #include "postgres.h"
 
-#include "access/genam.h"
-#include "access/htup_details.h"
 #include "access/table.h"
 #include "catalog/catalog.h"
 #include "catalog/indexing.h"
@@ -153,6 +151,15 @@ LargeObjectDrop(Oid loid)
  */
 bool
 LargeObjectExists(Oid loid)
+{
+	return LargeObjectExistsWithSnapshot(loid, NULL);
+}
+
+/*
+ * Same as LargeObjectExists(), except snapshot to read with can be specified.
+ */
+bool
+LargeObjectExistsWithSnapshot(Oid loid, Snapshot snapshot)
 {
 	Relation	pg_lo_meta;
 	ScanKeyData skey[1];
@@ -170,7 +177,7 @@ LargeObjectExists(Oid loid)
 
 	sd = systable_beginscan(pg_lo_meta,
 							LargeObjectMetadataOidIndexId, true,
-							NULL, 1, skey);
+							snapshot, 1, skey);
 
 	tuple = systable_getnext(sd);
 	if (HeapTupleIsValid(tuple))

src/backend/storage/large_object/inv_api.c

@@ -41,7 +41,6 @@
 #include "catalog/indexing.h"
 #include "catalog/objectaccess.h"
 #include "catalog/pg_largeobject.h"
-#include "catalog/pg_largeobject_metadata.h"
 #include "libpq/libpq-fs.h"
 #include "miscadmin.h"
 #include "storage/large_object.h"
@@ -123,43 +122,6 @@ close_lo_relation(bool isCommit)
 }
 
 
-/*
- * Same as pg_largeobject.c's LargeObjectExists(), except snapshot to
- * read with can be specified.
- */
-static bool
-myLargeObjectExists(Oid loid, Snapshot snapshot)
-{
-	Relation	pg_lo_meta;
-	ScanKeyData skey[1];
-	SysScanDesc sd;
-	HeapTuple	tuple;
-	bool		retval = false;
-
-	ScanKeyInit(&skey[0],
-				Anum_pg_largeobject_metadata_oid,
-				BTEqualStrategyNumber, F_OIDEQ,
-				ObjectIdGetDatum(loid));
-
-	pg_lo_meta = table_open(LargeObjectMetadataRelationId,
-							AccessShareLock);
-
-	sd = systable_beginscan(pg_lo_meta,
-							LargeObjectMetadataOidIndexId, true,
-							snapshot, 1, skey);
-
-	tuple = systable_getnext(sd);
-	if (HeapTupleIsValid(tuple))
-		retval = true;
-
-	systable_endscan(sd);
-
-	table_close(pg_lo_meta, AccessShareLock);
-
-	return retval;
-}
-
-
 /*
  * Extract data field from a pg_largeobject tuple, detoasting if needed
  * and verifying that the length is sane.  Returns data pointer (a bytea *),
@@ -279,7 +241,7 @@ inv_open(Oid lobjId, int flags, MemoryContext mcxt)
 		snapshot = GetActiveSnapshot();
 
 	/* Can't use LargeObjectExists here because we need to specify snapshot */
-	if (!myLargeObjectExists(lobjId, snapshot))
+	if (!LargeObjectExistsWithSnapshot(lobjId, snapshot))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_OBJECT),
 				 errmsg("large object %u does not exist", lobjId)));

src/include/catalog/pg_largeobject.h

@@ -20,6 +20,7 @@
 
 #include "catalog/genbki.h"
 #include "catalog/pg_largeobject_d.h"
+#include "utils/snapshot.h"
 
 /* ----------------
  *		pg_largeobject definition.  cpp turns this into
@@ -49,5 +50,6 @@ DECLARE_UNIQUE_INDEX_PKEY(pg_largeobject_loid_pn_index, 2683, LargeObjectLOidPNI
 extern Oid	LargeObjectCreate(Oid loid);
 extern void LargeObjectDrop(Oid loid);
 extern bool LargeObjectExists(Oid loid);
+extern bool LargeObjectExistsWithSnapshot(Oid loid, Snapshot snapshot);
 
 #endif							/* PG_LARGEOBJECT_H */