Function RelationGetStatExtList

src/backend/utils/cache/relcache.c:5061–5123

* RelationGetStatExtList * get a list of OIDs of statistics objects on this relation * * The statistics list is created only if someone requests it, in a way * similar to RelationGetIndexList(). We scan pg_statistic_ext to find * relevant statistics, and add the list to the relcache entry so that we * won't have to compute it again. Note that shared cache inval of a * relcache entry will

 * statistics, and syscache lookup could cause SI messages to be processed!
 */
List *
RelationGetStatExtList(Relation relation)
{
	Relation	indrel;
	SysScanDesc indscan;
	ScanKeyData skey;
	HeapTuple	htup;
	List	   *result;
	List	   *oldlist;
	MemoryContext oldcxt;

	/* Quick exit if we already computed the list. */
	if (relation->rd_statvalid != 0)
		return list_copy(relation->rd_statlist);

	/*
	 * We build the list we intend to return (in the caller's context) while
	 * doing the scan.  After successfully completing the scan, we copy that
	 * list into the relcache entry.  This avoids cache-context memory leakage
	 * if we get some sort of error partway through.
	 */
	result = NIL;

	/*
	 * Prepare to scan pg_statistic_ext for entries having stxrelid = this
	 * rel.
	 */
	ScanKeyInit(&skey,
				Anum_pg_statistic_ext_stxrelid,
				BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(RelationGetRelid(relation)));

	indrel = table_open(StatisticExtRelationId, AccessShareLock);
	indscan = systable_beginscan(indrel, StatisticExtRelidIndexId, true,
								 NULL, 1, &skey);

	while (HeapTupleIsValid(htup = systable_getnext(indscan)))
	{
		Oid			oid = ((Form_pg_statistic_ext) GETSTRUCT(htup))->oid;

		result = lappend_oid(result, oid);
	}

	systable_endscan(indscan);

	table_close(indrel, AccessShareLock);

	/* Sort the result list into OID order, per API spec. */
	list_sort(result, list_oid_cmp);

	/* Now save a copy of the completed list in the relcache entry. */
	oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
	oldlist = relation->rd_statlist;
	relation->rd_statlist = list_copy(result);

	relation->rd_statvalid = true;
	MemoryContextSwitchTo(oldcxt);