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From "Mikhail Bautin (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-3976) Disable Block Cache On Compactions
Date Wed, 18 Jan 2012 22:56:39 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3976?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13188784#comment-13188784
] 

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

The last commit I can see for this JIRA is the following:

{quote}

Author: stack <stack@13f79535-47bb-0310-9956-ffa450edef68>
Date:   Tue Jun 14 16:47:37 2011
  
    HBASE-3976 Disable Block Cache On Compactions -- REVERT
{quote}

This makes me think this path was actually reverted in trunk. Besides, when Jonathan's HBASE-4422
(CacheConfig) went in, it completely changed the way this feature would be implemented. This
is why it is not possible to verify whether the patch has been applied or not anymore from
looking at the current version of Store.java in trunk. I can't say off the top of my head
whether we cache blocks on write during compactions in HBase trunk these days with the new
logic implemented by HBASE-4422 in effect. However, I am planning to write a new unit test
for both trunk and 89-fb to verify that, and address this JIRA if necessary in a consistent
way across the two branches.

                
> 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: Nicolas Spiegelberg
>            Priority: Minor
>         Attachments: HBASE-3976-V3.patch, HBASE-3976-unconditional.patch, HBASE-3976.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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