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From "Ted Yu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18085) Prevent parallel purge in ObjectPool
Date Sun, 21 May 2017 08:51:04 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18085?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16018762#comment-16018762
] 

Ted Yu commented on HBASE-18085:
--------------------------------

>From https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/locks/ReentrantLock.html
:

bq. Also note that the untimed tryLock method does not honor the fairness setting. It will
succeed if the lock is available even if other threads are waiting.

Should the timed version of tryLock be used ?

> 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, HBASE-18085.patch
>
>
> 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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