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https://issues.apache.org/jira/browse/HBASE-17057?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15703800#comment-15703800
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Ashu Pachauri edited comment on HBASE-17057 at 11/29/16 1:59 AM:
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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 compactions is tied 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.
was (Author: ashu210890):
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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