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From "Mikhail Bautin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-3976) Disable Block Cache On Compactions
Date Wed, 05 Sep 2012 06:27:08 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3976?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13448521#comment-13448521
] 

Mikhail Bautin commented on HBASE-3976:
---------------------------------------

Lars: I agree, cache-on-flush is definitely the most useful. This is what we are now using
in production for some workloads.
                
> Disable Block Cache On Compactions
> ----------------------------------
>
>                 Key: HBASE-3976
>                 URL: https://issues.apache.org/jira/browse/HBASE-3976
>             Project: HBase
>          Issue Type: Improvement
>          Components: regionserver
>    Affects Versions: 0.90.3
>            Reporter: Karthick Sankarachary
>            Assignee: Mikhail Bautin
>            Priority: Minor
>         Attachments: HBASE-3976.patch, HBASE-3976-unconditional.patch, HBASE-3976-V3.patch
>
>
> Is there a good reason to believe that caching blocks during compactions is beneficial?
Currently, if block cache is enabled on a certain family, then every time it's compacted,
we load all of its blocks into the (LRU) cache, at the expense of the legitimately hot ones.
> As a matter of fact, this concern was raised earlier in HBASE-1597, which rightly points
out that, "we should not bog down the LRU with unneccessary blocks" during compaction. Even
though that issue has been marked as "fixed", it looks like it ought to be reopened.
> Should we err on the side of caution and not cache blocks during compactions period (as
illustrated in the attached patch)? Or, can we be selectively aggressive about what blocks
do get cached during compaction (e.g., only cache those blocks from the recent files)?

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