[jboss-jira] [JBoss JIRA] (WFLY-12581) Optimize web/ejb expiration schedulers

[Paul Ferraro (Jira)]

Paul Ferraro created WFLY-12581:
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             Summary: Optimize web/ejb expiration schedulers
                 Key: WFLY-12581
                 URL: https://issues.jboss.org/browse/WFLY-12581
             Project: WildFly
          Issue Type: Enhancement
          Components: Clustering
    Affects Versions: 18.0.0.Beta1
            Reporter: Paul Ferraro
            Assignee: Paul Ferraro


WF18 added a new expiration scheduler implementation for SFSBs specifically optimized for non-distributed environments.  The key features of this implementations are:
* Uses a single scheduled task instead of a scheduled task per SFSB
* Uses a double-linked list to track SFSBs to be expired

The use of a linked queue is based on the following assumptions:
# All SFSB using a given scheduler share the same @StatefulTimeout
# A given call to Scheduler.schedule(...) is always the last item to be scheduled

Distributed SFSBs cannot use the same implementation because the second assumption is not valid, as a member may assume the responsibility of expiring a SFSB previously owned by another member.  They can, however, leverage the strategy of using a single scheduled task instead of a task per SFSB.  Due to the nature of the scheduler, that most scheduled tasks will be cancelled/removed and rescheduled, this strategy outperforms the current implementation.

This jira proposes the following:
* Generalize the Scheduler interface for reuse between SFSBs and web sessions.
* Generalize the new local scheduler implementation such that the same scheduler can support both local and distributed SFSBs using different queue implementations for tracking scheduled items
* Distributed use case uses a PriorityBlockingQueue, which has O(log N) add/remove characteristics
* Replace ExpirationTracker with a ConcurrentDirectDeque to support local case, which has O(1) add/remove characteristics
** ConcurrentDirectDeque outperforms ExpirationTracker under concurrent load

Local web session expiration cannot use the same expiration scheduler used by local SFSBs because the first assumption is not valid, since a given web session can override the default max inactive interval.  However, we can still optimize the local web session case by delegating expiration to the PriorityBlockingQueue-based implementation if the session uses a non-default max inactive interval, and to the ConcurrentDirectDeque-based implementation if the session uses the default max inactive interval.



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