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From "Jonathan Gray (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (HBASE-3322) HLog sync slowdown under heavy load with HBASE-2467
Date Mon, 21 Mar 2011 21:54:06 GMT

     [ https://issues.apache.org/jira/browse/HBASE-3322?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Jonathan Gray resolved HBASE-3322.

    Resolution: Won't Fix

There is an issue here but upon further investigation, it's not really a bug.

The issue is around heavy concurrency / high number of threads in HLog.  The current behavior
is that each thread does a notify to the LogSyncer and then does a wait on a single object.
 The LogSyncer waits to be notified, then syncs what is pending, and then does a notifyAll
to all the threads waiting for their sync.

This is a straightforward and correct pattern but under heavy concurrency, the fact that all
threads are waiting on a single object to be notified becomes a bottleneck.

Will open other JIRAs to deal with solutions to this.  Closing this one as this is not a blocking

> HLog sync slowdown under heavy load with HBASE-2467
> ---------------------------------------------------
>                 Key: HBASE-3322
>                 URL: https://issues.apache.org/jira/browse/HBASE-3322
>             Project: HBase
>          Issue Type: Bug
>          Components: io, regionserver
>    Affects Versions: 0.90.0
>            Reporter: Jonathan Gray
>            Priority: Blocker
>             Fix For: 0.92.0
> Testing HBASE-2467 and HDFS-895 on 100 node cluster w/ a heavy increment workload we
experienced significant slowdown.
> Stack traces show that most threads are on HLog.updateLock.

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