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Message-ID: <3093814.36701274567241383.JavaMail.jira@thor>
Date: Sat, 22 May 2010 18:27:21 -0400 (EDT)
From: "Andrew Purtell (JIRA)" <jira@apache.org>
To: hbase-issues@hadoop.apache.org
Subject: [jira] Commented: (HBASE-2468) Improvements to prewarm META cache
 on clients
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    [ https://issues.apache.org/jira/browse/HBASE-2468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12870326#action_12870326 ] 

Andrew Purtell commented on HBASE-2468:
---------------------------------------

bq. I agree with Jonathan that the "prefetch entire META" should be optional, default false. 

Well you are the reporter so I will defer to that, though the issue description implies otherwise to me. 


> Improvements to prewarm META cache on clients
> ---------------------------------------------
>
>                 Key: HBASE-2468
>                 URL: https://issues.apache.org/jira/browse/HBASE-2468
>             Project: Hadoop HBase
>          Issue Type: Improvement
>          Components: client
>            Reporter: Todd Lipcon
>            Assignee: Mingjie Lai
>             Fix For: 0.21.0
>
>         Attachments: HBASE-2468-trunk.patch
>
>
> A couple different use cases cause storms of reads to META during startup. For example, a large MR job will cause each map task to hit meta since it starts with an empty cache.
> A couple possible improvements have been proposed:
>  - MR jobs could ship a copy of META for the table in the DistributedCache
>  - Clients could prewarm cache by doing a large scan of all the meta for the table instead of random reads for each miss
>  - Each miss could fetch ahead some number of rows in META

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