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https://issues.apache.org/jira/browse/HBASE-7336?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13529669#comment-13529669
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stack commented on HBASE-7336:
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Should the tryLock have a timeout on it?
Else patch is an improvement for sure worth committing till we do better.
I wonder what the difference is if more than one Reader.
Looking at hdfs, each open goes to the namenode so can't open a reader per
scanner... would cost a bit on setup? If we could distingush short from long
scan we could do pread on the shorts and open a reader per Scanner for the long
runners?
> 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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