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From "Vladimir Rodionov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7336) HFileBlock.readAtOffset does not work well with multiple threads
Date Tue, 15 Jul 2014 23:01:08 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7336?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14062814#comment-14062814
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Vladimir Rodionov commented on HBASE-7336:
------------------------------------------

I monitor thread stack traces during test run. Usually, just one thread (Scanner) is running,
all others are waiting on DFSInputStream in some places (as I said, too many synchronized
methods). This is HDFS, not HBase.

> HFileBlock.readAtOffset does not work well with multiple threads
> ----------------------------------------------------------------
>
>                 Key: HBASE-7336
>                 URL: https://issues.apache.org/jira/browse/HBASE-7336
>             Project: HBase
>          Issue Type: Sub-task
>          Components: Performance
>            Reporter: Lars Hofhansl
>            Assignee: Lars Hofhansl
>            Priority: Critical
>             Fix For: 0.94.4, 0.95.0
>
>         Attachments: 7336-0.94.txt, 7336-0.96.txt
>
>
> HBase grinds to a halt when many threads scan along the same set of blocks and neither
read short circuit is nor block caching is enabled for the dfs client ... disabling the block
cache makes sense on very large scans.
> It turns out that synchronizing in istream in HFileBlock.readAtOffset is the culprit.



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