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From "Anoop Sam John (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18085) Prevent parallel purge in ObjectPool
Date Sat, 20 May 2017 16:39:04 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18085?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16018537#comment-16018537

Anoop Sam John commented on HBASE-18085:

Good find and ur point make sense. We should just come out of purge call when already a purge
in progress.  As per impl, we should need a boolean state indicating the status of run and
which needs to be volatile (?) Then again we have a perf cost here.  May be we should take
a new approach all together?   Than calling purge on every call to getLock()?

> Prevent parallel purge in ObjectPool
> ------------------------------------
>                 Key: HBASE-18085
>                 URL: https://issues.apache.org/jira/browse/HBASE-18085
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Yu Li
>            Assignee: Yu Li
>         Attachments: e89l05465.st3.jstack
> Parallel purge in ObjectPool is meaningless and will cause contention issue since {{ReferenceQueue#poll}}
has synchronization (source code shown below)
> {code}
>     public Reference<? extends T> poll() {
>         if (head == null)
>             return null;
>         synchronized (lock) {
>             return reallyPoll();
>         }
>     }
> {code}
> We observed threads blocking on the purge method while using offheap bucket cache, and
we could easily reproduce this by testing the 100% cache hit case in bucket cache with enough
reading threads.
> We propose to add a purgeLock and use tryLock to avoid parallel purge.

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