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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 Fri, 25 Jul 2014 20:10:40 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7336?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14074849#comment-14074849
] 

Vladimir Rodionov commented on HBASE-7336:
------------------------------------------

[~lhofhansl]

The major priority right now is to improve compaction and normal operations during compaction.
Sure we need to track region stats to make optimal inter-region splits, but even without such
a stats we can decrease data skew significantly. 

> 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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