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From "Yu Li (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18085) Prevent parallel purge in ObjectPool
Date Tue, 23 May 2017 07:36:04 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18085?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16020766#comment-16020766
] 

Yu Li commented on HBASE-18085:
-------------------------------

Referring to this [post|http://java-performance.info/jmh/], we need a non-local state variable
to avoid JIT optimization, so I changed the testLock method as below:
{code}
  private boolean blackHoleVal;

  @Benchmark
  public void testLock(Blackhole bh) {
    boolean attained = purgeLock.tryLock();
    blackHoleVal = attained;
    try {
      // do purge
      bh.consume(blackHoleVal);
      return;
    } finally {
      if (attained) {
        purgeLock.unlock();
      }
    }
  }
{code}
And get a more reasonable result (the previous result was not that reasonable considering
the underlying implementation of ReentrantLock#tryLock):
{noformat}
Benchmark                                 Mode  Cnt         Score         Error  Units
AtomicLockBenchmark.testAtomicBoolean    thrpt  100  47314035.981 ± 1418461.917  ops/s
AtomicLockBenchmark.testLock             thrpt  100  47139427.031 ±  677362.892  ops/s
AtomicLockBenchmark.testVolatileBoolean  thrpt  100  45676053.492 ±  786938.305  ops/s
{noformat}

> 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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