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Date: Wed, 16 Sep 2015 03:22:45 +0000 (UTC)
From: "stack (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Commented] (HBASE-14383) Compaction improvements
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    [ https://issues.apache.org/jira/browse/HBASE-14383?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14746749#comment-14746749 ] 

stack commented on HBASE-14383:
-------------------------------

I'd be for upping the max logs number (have seen cases where it ran away up to the thousands so some guard would be good)

> Compaction improvements
> -----------------------
>
>                 Key: HBASE-14383
>                 URL: https://issues.apache.org/jira/browse/HBASE-14383
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Vladimir Rodionov
>            Assignee: Vladimir Rodionov
>             Fix For: 2.0.0
>
>
> Still major issue in many production environments. The general recommendation - disabling region splitting and major compactions to reduce unpredictable IO/CPU spikes, especially during peak times and running them manually during off peak times. Still do not resolve the issues completely.
> h3. Flush storms
> * rolling WAL events across cluster can be highly correlated, hence flushing memstores, hence triggering minor compactions, that can be promoted to major ones. These events are highly correlated in time if there is a balanced write-load on the regions in a table.
> *  the same is true for memstore flushing due to periodic memstore flusher operation. 
> Both above may produce *flush storms* which are as bad as *compaction storms*. 
> What can be done here. We can spread these events over time by randomizing (with jitter) several  config options:
> # hbase.regionserver.optionalcacheflushinterval
> # hbase.regionserver.flush.per.changes
> # hbase.regionserver.maxlogs   
> h3. ExploringCompactionPolicy max compaction size
> One more optimization can be added to ExploringCompactionPolicy. To limit size of a compaction there is a config parameter one could use hbase.hstore.compaction.max.size. It would be nice to have two separate limits: for peak and off peak hours.
> h3. ExploringCompactionPolicy selection evaluation algorithm
> Too simple? Selection with more files always wins, selection of smaller size wins if number of files is the same. 


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