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From "HBase Review Board (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2468) Improvements to prewarm META cache on clients
Date Thu, 10 Jun 2010 16:03:14 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12877462#action_12877462
] 

HBase Review Board commented on HBASE-2468:
-------------------------------------------

Message from: "Todd Lipcon" <todd@cloudera.com>


bq.  On 2010-06-10 08:53:41, Jonathan Gray wrote:
bq.  > src/main/java/org/apache/hadoop/hbase/client/MetaScanner.java, line 109
bq.  > <http://review.hbase.org/r/98/diff/5/?file=944#file944line109>
bq.  >
bq.  >     Hmm, wouldn't that be Math.min then?  If rowLimit = 5 and scanner.caching =
100, we want to only do 5?

woops, yes :)


- Todd


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> Improvements to prewarm META cache on clients
> ---------------------------------------------
>
>                 Key: HBASE-2468
>                 URL: https://issues.apache.org/jira/browse/HBASE-2468
>             Project: 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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