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From "Jonathan Gray (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1597) Prevent unnecessary caching of blocks during compactions
Date Wed, 01 Jul 2009 05:04:47 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1597?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12725923#action_12725923

Jonathan Gray commented on HBASE-1597:

Currently tied to 0.20.0 until we investigate further.  Ryan, what say you?

> Prevent unnecessary caching of blocks during compactions
> --------------------------------------------------------
>                 Key: HBASE-1597
>                 URL: https://issues.apache.org/jira/browse/HBASE-1597
>             Project: Hadoop HBase
>          Issue Type: Bug
>    Affects Versions: 0.20.0
>            Reporter: Jonathan Gray
>             Fix For: 0.20.0
> When running any kind of compaction, we read every block of every storefile being compacted
into the block cache.
> We would like to reuse any already cached blocks, if available, but otherwise we should
not bog down the LRU with unnecessary blocks.
> This is not as bad as it was with the old LRU because the latest LRU implementation (HBASE-1460)
is scan-resistant.  This ensures that we are not causing massive eviction of the blocks that
are being read multiple times or from in-memory tables.  However, this does add to the GC-woes
of an import because each block gets further referenced, and for longer periods of time. 
There is also overhead in running the LRU evictions.

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