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From "Nick Dimiduk (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-11558) Caching set on Scan object gets lost when using TableMapReduceUtil in 0.95+
Date Wed, 30 Jul 2014 20:28:41 GMT

    [ https://issues.apache.org/jira/browse/HBASE-11558?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14079920#comment-14079920
] 

Nick Dimiduk commented on HBASE-11558:
--------------------------------------

+1 for patch v2.

TestStripeCompactionPolicy and TestDefaultCompactSelection both pass for me locally. Will
commit.

> Caching set on Scan object gets lost when using TableMapReduceUtil in 0.95+
> ---------------------------------------------------------------------------
>
>                 Key: HBASE-11558
>                 URL: https://issues.apache.org/jira/browse/HBASE-11558
>             Project: HBase
>          Issue Type: Bug
>          Components: mapreduce, Scanners
>            Reporter: Ishan Chhabra
>            Assignee: Ishan Chhabra
>             Fix For: 0.99.0, 0.96.3, 0.98.5, 2.0.0
>
>         Attachments: HBASE_11558-0.96.patch, HBASE_11558-0.96_v2.patch, HBASE_11558-0.98.patch,
HBASE_11558-0.98_v2.patch, HBASE_11558.patch, HBASE_11558_v2.patch, HBASE_11558_v2.patch
>
>
> 0.94 and before, if one sets caching on the Scan object in the Job by calling scan.setCaching(int)
and passes it to TableMapReduceUtil, it is correctly read and used by the mappers during a
mapreduce job. This is because Scan.write respects and serializes caching, which is used internally
by TableMapReduceUtil to serialize and transfer the scan object to the mappers.
> 0.95+, after the move to protobuf, ProtobufUtil.toScan does not respect caching anymore
as ClientProtos.Scan does not have the field caching. Caching is passed via the ScanRequest
object to the server and so is not needed in the Scan object. However, this breaks application
code that relies on the earlier behavior. This will lead to sudden degradation in Scan performance
0.96+ for users relying on the old behavior.
> There are 2 options here:
> 1. Add caching to Scan object, adding an extra int to the payload for the Scan object
which is really not needed in the general case.
> 2. Document and preach that TableMapReduceUtil.setScannerCaching must be called by the
client.



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