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From "Ashu Pachauri (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17057) Minor compactions should also drop page cache behind reads
Date Tue, 29 Nov 2016 01:29:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17057?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15703800#comment-15703800
] 

Ashu Pachauri commented on HBASE-17057:
---------------------------------------

I had a first look at the code, things never are straightforward in the land of compactions.

1. Whether we can drop cache behind reads/writes for compaction is tried to whether we should
throttle compactions. Not sure what dropping page cache has to do with throttling compactions.
[~eclark] , can you shed a little light on why this is the case? (Since you added this piece
of code in HBASE-14098 )
2. It seems that we just ignore drop cache hint for all compactions on master branch. I'll
dig more and try to find why the behavior was modified on master.

> Minor compactions should also drop page cache behind reads
> ----------------------------------------------------------
>
>                 Key: HBASE-17057
>                 URL: https://issues.apache.org/jira/browse/HBASE-17057
>             Project: HBase
>          Issue Type: Improvement
>          Components: Compaction
>            Reporter: Ashu Pachauri
>            Assignee: Ashu Pachauri
>
> Long compactions currently drop cache behind reads so that they don't pollute the page
cache but short compactions don't do that. The bulk of the data is actually read during minor
compactions instead of major compactions,  and thrashes the page cache since it's mostly not
needed. 
> We should drop page cache behind reads for minor compactions too. 



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