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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7336) HFileBlock.readAtOffset does not work well with multiple threads
Date Sun, 16 Nov 2014 06:53:34 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7336?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14213870#comment-14213870
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Lars Hofhansl commented on HBASE-7336:
--------------------------------------

[~vrodionov], I have a quite simple patch that would allow compaction to have their own, private
readers. With what you've seen, would that be a benefit?

> 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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