Function IndexScanOK

src/backend/utils/cache/catcache.c:1084–1133

* IndexScanOK * * This function checks for tuples that will be fetched by * IndexSupportInitialize() during relcache initialization for * certain system indexes that support critical syscaches. * We can't use an indexscan to fetch these, else we'll get into * infinite recursion. A plain heap scan will work, however. * Once we have completed relcache initialization (signaled by * c

 *		catalogs' indexes.
 */
static bool
IndexScanOK(CatCache *cache, ScanKey cur_skey)
{
	switch (cache->id)
	{
		case INDEXRELID:

			/*
			 * Rather than tracking exactly which indexes have to be loaded
			 * before we can use indexscans (which changes from time to time),
			 * just force all pg_index searches to be heap scans until we've
			 * built the critical relcaches.
			 */
			if (!criticalRelcachesBuilt)
				return false;
			break;

		case AMOID:
		case AMNAME:

			/*
			 * Always do heap scans in pg_am, because it's so small there's
			 * not much point in an indexscan anyway.  We *must* do this when
			 * initially building critical relcache entries, but we might as
			 * well just always do it.
			 */
			return false;

		case AUTHNAME:
		case AUTHOID:
		case AUTHMEMMEMROLE:
		case DATABASEOID:
		case PROFILEID:
		case PROFILENAME:

			/*
			 * Protect authentication lookups occurring before relcache has
			 * collected entries for shared indexes.
			 */
			if (!criticalSharedRelcachesBuilt)
				return false;
			break;

		default:
			break;
	}

	/* Normal case, allow index scan */
	return true;
}

/*
 * This function performs checks for certain system tables to validate tuple