Function load_enum_cache_data

src/backend/utils/cache/typcache.c:2628–2778

* Load (or re-load) the enumData member of the typcache entry. */

 * Load (or re-load) the enumData member of the typcache entry.
 */
static void
load_enum_cache_data(TypeCacheEntry *tcache)
{
	TypeCacheEnumData *enumdata;
	Relation	enum_rel;
	SysScanDesc enum_scan;
	HeapTuple	enum_tuple;
	ScanKeyData skey;
	EnumItem   *items;
	int			numitems;
	int			maxitems;
	Oid			bitmap_base;
	Bitmapset  *bitmap;
	MemoryContext oldcxt;
	int			bm_size,
				start_pos;

	/* Check that this is actually an enum */
	if (tcache->typtype != TYPTYPE_ENUM)
		ereport(ERROR,
				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
				 errmsg("%s is not an enum",
						format_type_be(tcache->type_id))));

	/*
	 * Read all the information for members of the enum type.  We collect the
	 * info in working memory in the caller's context, and then transfer it to
	 * permanent memory in CacheMemoryContext.  This minimizes the risk of
	 * leaking memory from CacheMemoryContext in the event of an error partway
	 * through.
	 */
	maxitems = 64;
	items = (EnumItem *) palloc(sizeof(EnumItem) * maxitems);
	numitems = 0;

	/* Scan pg_enum for the members of the target enum type. */
	ScanKeyInit(&skey,
				Anum_pg_enum_enumtypid,
				BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(tcache->type_id));

	enum_rel = table_open(EnumRelationId, AccessShareLock);
	enum_scan = systable_beginscan(enum_rel,
								   EnumTypIdLabelIndexId,
								   true, NULL,
								   1, &skey);

	while (HeapTupleIsValid(enum_tuple = systable_getnext(enum_scan)))
	{
		Form_pg_enum en = (Form_pg_enum) GETSTRUCT(enum_tuple);

		if (numitems >= maxitems)
		{
			maxitems *= 2;
			items = (EnumItem *) repalloc(items, sizeof(EnumItem) * maxitems);
		}
		items[numitems].enum_oid = en->oid;
		items[numitems].sort_order = en->enumsortorder;