[jira] [Comment Edited] (HBASE-7336) HFileBlock.readAtOffset does not work well with multiple threads

["Lars Hofhansl (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-7336?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13530580#comment-13530580 ] 

Lars Hofhansl edited comment on HBASE-7336 at 12/13/12 1:33 AM:
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Numbers with patch and read short circuit enabled for completeness:
One client: 15s (104%)
Two clients: 22s (180% CPU)

                
      was (Author: lhofhansl):
    Numbers with patch and read short circuit enabled for completeness:
One client: 15s
Two clients: 22s

(same as without short circuiting)
                  
> 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: Bug
>            Reporter: Lars Hofhansl
>            Assignee: Lars Hofhansl
>            Priority: Critical
>             Fix For: 0.96.0, 0.94.4
>
>         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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