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https://issues.apache.org/jira/browse/HBASE-5000?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13166608#comment-13166608
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stack commented on HBASE-5000:
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I agree this priority minor. We should probably add to the book that currently
disabling block cache completed is not recommended.
> Speed up simultaneous reads of a block when block caching is turned off
> -----------------------------------------------------------------------
>
> Key: HBASE-5000
> URL: https://issues.apache.org/jira/browse/HBASE-5000
> Project: HBase
> Issue Type: Bug
> Reporter: Mikhail Bautin
> Priority: Minor
>
> With block caching, when one client starts reading a block and another one
> comes around asking for the same block, the second client waits for the first
> one to finish reading and returns the block from cache. This is achieved by
> locking on the block offset using IdLock, a "sparse lock" primitive allowing
> to lock on arbitrary long numbers. However, in case there is no block
> caching, there is no reason to wait for other clients that are reading the
> same block. One challenge optimizing this that we don't necessary have
> accurate information about whether other HFile API clients interested in the
> block would cache it.
> Setting priority as minor, as it is very unusual to turn off block caching.
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