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Date: Fri, 10 Sep 2010 13:32:33 -0400 (EDT)
From: "Todd Lipcon (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
Subject: [jira] Commented: (HBASE-2981) Improve consistency of performance
 during heavy load
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    [ https://issues.apache.org/jira/browse/HBASE-2981?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12908104#action_12908104 ] 

Todd Lipcon commented on HBASE-2981:
------------------------------------

One case of blocking is when a region hits the blocking store files limit. In current versions, once a region it hits the limit, it enters the compaction queue at the back. So if there are other compactions already in the queue, it can take some time before the blocked region gets unblocked, since it's waiting on all the other compactions.

I think a similar thing can happen with the flushes that happen around a close or split.

If we prioritize compactions (HBASE-2646) we can make these compactions that block progress take precedence over normal "maintenance" compactions.

> Improve consistency of performance during heavy load
> ----------------------------------------------------
>
>                 Key: HBASE-2981
>                 URL: https://issues.apache.org/jira/browse/HBASE-2981
>             Project: HBase
>          Issue Type: Task
>          Components: regionserver
>            Reporter: Todd Lipcon
>
> Currently when running load tests like YCSB, we experience periods of complete cluster inactivity while all clients are blocked on a single region which is unavailable.
> As discussed recently on the list, we should brainstorm some ideas for how to improve the situation: the goal here is to (a) minimize the amount of time when a region is inaccessible, and (b) minimize the impact that one inaccessible region has on other operations in the cluster.

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