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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 Wed, 09 Jun 2010 22:56:14 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12877251#action_12877251
] 

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

Message from: "Mingjie Lai" <mjlai09@gmail.com>

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This is an automatically generated e-mail. To reply, visit:
http://review.hbase.org/r/98/
-----------------------------------------------------------

(Updated 2010-06-09 15:50:59.084657)


Review request for hbase, Todd Lipcon and stack.


Changes
-------

@St^ack: please see my comments for your feedback regarding getRowOrBefore() issue. 

Invite Todd as a reviewer. 


Summary
-------

HBASE-2468: Improvements to prewarm META cache on clients.

Changes:
1. Add new HTable methods which support region info de/serialation, and region cache prewarm:

- void serializeRegionInfo(): clients could perform a large scan for all the meta for the
table, serialize the meta to a file. MR job can ship a copy of the meta for the table in the
DistributedCache
- Map<HRegionInfo, HServerAddress> deserializeRegionInfo(): MR job can deserialize the
region info from the DistributedCache 
- prewarmRegionCache(Map<HRegionInfo, HServerAddress> regionMap): MR job can prewarm
local region cache by the deserialized region info.

2. For each client, each region cache read-miss could trigger read-ahead some number of rows
in META. This option could be turned on and off for one particular table. 


This addresses bug HBASE-2468.
    http://issues.apache.org/jira/browse/HBASE-2468


Diffs
-----

  src/main/java/org/apache/hadoop/hbase/client/HConnection.java 853164d 
  src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java ed18092 
  src/main/java/org/apache/hadoop/hbase/client/HTable.java 7ec95cb 
  src/main/java/org/apache/hadoop/hbase/client/MetaScanner.java d3a0c07 
  src/test/java/org/apache/hadoop/hbase/client/TestFromClientSide.java 95e494a 

Diff: http://review.hbase.org/r/98/diff


Testing
-------

Unit tests passed locally for me. 


Thanks,

Mingjie




> 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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