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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 Thu, 31 Jul 2014 01:20:39 GMT

    [ https://issues.apache.org/jira/browse/HBASE-11558?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14080352#comment-14080352
] 

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

Thanks, looks good.

Go ahead and open the ticket. Should be deprecated on 0.98 and branch-1, removed from master.
In addition to the deprecation annotations on Java methods, we should WARN when the config
is used.

> 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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