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Date: Tue, 29 Nov 2016 01:29:58 +0000 (UTC)
From: "Ashu Pachauri (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Commented] (HBASE-17057) Minor compactions should also drop
 page cache behind reads
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archived-at: Tue, 29 Nov 2016 01:30:01 -0000


    [ 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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