[jira] Commented: (HBASE-2468) Improvements to prewarm META cache on clients

["HBase Review Board (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-2468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12873849#action_12873849 ] 

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

Message from: "Mingjie Lai" <mj...@gmail.com>


bq.  On 2010-05-28 15:05:08, Ryan Rawson wrote:
bq.  > src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java, line 1604
bq.  > <http://review.hbase.org/r/98/diff/3/?file=741#file741line1604>
bq.  >
bq.  >     What does this method actually do? If its a predicate start it with 'is'.  Also precaching should be off by default...
bq.  >      Is it?

Will add ``is'' prefix to this method. 

Pre-caching (in case of a cache miss) is set to ``on'' by default right now, according to stack:

``I'm for default behavior being grabbing more than just the one row – ten or something. Regards full-table scan as default, I think it should be an option (Its a nice option to have). ''

https://issues.apache.org/jira/browse/HBASE-2468?focusedCommentId=12870321&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#action_12870321


- Mingjie


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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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