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

[Bela Ban (JIRA)]

STATE: queue requests during state transfer
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                 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: 3.1


STATE should queue requests to be delivered to the application while a state transfer is in progress.

Draft design:

- On STATE-REQ:
  - If busy --> add request to queue, return
  - Else --> processRequest
  - Close MessageQueue and deliver all messages in it to the application
  - Kick off a STABLE round, wait until it completes
  - If MessageQueue is not empty --> processRequests()

- processRequest():
  - Close BARRIER, suspend STABLE
  - Get digest
  - Open MessageQueue: all new messages 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)

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 ?)

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