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https://issues.apache.org/jira/browse/HBASE-7336?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13529712#comment-13529712
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stack commented on HBASE-7336:
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bq. tryLock without a timeout returns immediately.
Sorry. Thought for some reason it waited.
bq. How many, though? And I am not sure how this would interact with the block
cache (would probably be OK).
One per scanner? Can we look at a scanner and figure somehow if its long or
short? If start/stop row? Limit? Maybe allow someone pass a hint?
Compactions should go get their own Reader?
> 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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