HCP nodes can each process a maximum of five concurrent queries. If a query arrives at a node that is currently processing five queries, HCP queues the query and processes it as soon as the current queries are complete. A 503 (Service Unavailable) error code is only returned if so many queries are queued up that the node fails to deal with them in the maximum allotted wait time.
In response to a 503 error code, you should try the query again, gradually increasing the delay between each successive attempt.
© 2016 Hitachi Data Systems Corporation. All rights reserved.