Function TryGetCollectionShardTable

pg_documentdb/src/metadata/collection.c:570–597

* Given a collection, tries to get a shardOID if one is applicable (there is * a single shard corresponding to that collection) and if it's available * locally. If such a shard is found, locks it with the given lock mode * and returns it to the caller. */

 * and returns it to the caller.
 */
Oid
TryGetCollectionShardTable(MongoCollection *collection, LOCKMODE lockMode)
{
	/* Cannot proceed without a local shard available. */
	if (collection->shardTableName[0] == '\0')
	{
		return InvalidOid;
	}

	if (!UseLocalExecutionShardQueries)
	{
		return InvalidOid;
	}

	/* Don't allow direct shard access in a multi-statement transaction
	 * This is because switching states between remote execution and local execution can produce
	 * isolation issues. So only support this if we're a single command.
	 */
	if (IsTransactionBlock() && !ForceLocalExecutionShardQueries)
	{
		return InvalidOid;
	}

	Oid relationShardOid = GetRelationIdForCollectionTableName(collection->shardTableName,
															   lockMode);
	ereport(DEBUG3, (errmsg("Has relation shard: %d", relationShardOid != InvalidOid)));
	return relationShardOid;
}


static void