[jboss-jira] [JBoss JIRA] (JGRP-1352) StreamingStateTransfer: queue requests during state transfer

StreamingStateTransfer: queue requests during state transfer ------------------------------------------------------------ Key: JGRP-1352 URL: https://issues.jboss.org/browse/JGRP-1352 Project: JGroups Issue Type: Feature Request Reporter: Bela Ban Assignee: Bela Ban Fix For: 3.2 STATE should queue requests to be delivered to the application while a state transfer is in progress. Draft design: * MessageQueue: queue for application messages * STATE-REQ queue: queue for STATE-REQ requests * On STATE-REQ: ** If busy --> add request to STATE-REQ queue, return ** Else --> processRequest ** Close MessageQueue and deliver all messages in it to the application *** Regular message deliver needs to be blocked until all messages from the MessageQueue have been delivered ** Kick off a STABLE round, wait until it completes ** If STATE-REQ queue is not empty --> processRequests() * processRequest(): ** Close BARRIER, suspend STABLE ** Get digest ** Open MessageQueue: all new messages (MSG) will be queued now, rather than delivered to the application *** (Only MSG, not VIEW !) ** Open BARRIER (leave STABLE suspended !) ** Transfer state to state requester ** Resume STABLE Advantages: - The state provider is not blocked, e.g. to handle JOIN requests - Only the state *requester* is blocked, this is OK though - Between the state requests, the state provider gets a little breathing room to process queued-up messages, and to purge messages (through stability) - Disadvantages: - If *blocking* messages (e.g. RPCs) are queued, we won't be able to send responses back until the queue is drained Misc: - Should the MessageQueue use the disk to handle large message sets ? - If modifications are idempotent, we *don't* need to queue messages (make this configurable !) (for example Infinispan ?)