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https://issues.apache.org/jira/browse/HBASE-7336?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13531265#comment-13531265
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stack commented on HBASE-7336:
------------------------------
+1 on committing this for now.
On Reader per long-running scanner, it will complicate the swapping in of new
files on compaction but probably worth figuring out. Lets file issues for
further improvement.
Good stuff Lars.
> 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
> 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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