[jira] [Commented] (HBASE-14696) Support setting allowPartialResults in mapreduce Mappers

["Andrew Purtell (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-14696?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14988690#comment-14988690 ] 

Andrew Purtell commented on HBASE-14696:
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Why wasn't this committed to any releaseable branch? Doesn't do much good where it is right now. Picking it back. 

> Support setting allowPartialResults in mapreduce Mappers
> --------------------------------------------------------
>
>                 Key: HBASE-14696
>                 URL: https://issues.apache.org/jira/browse/HBASE-14696
>             Project: HBase
>          Issue Type: Improvement
>          Components: mapreduce
>    Affects Versions: 2.0.0, 1.1.0
>            Reporter: Mindaugas Kairys
>            Assignee: Ted Yu
>             Fix For: 2.0.0, 1.3.0
>
>         Attachments: 14696-branch-1-v1.txt, 14696-branch-1-v2.txt, 14696-branch-1-v2.txt, 14696-v1.txt, 14696-v2.txt
>
>
> It is currently impossible to get partial results in mapreduce mapper jobs.
> When setting setAllowPartialResults(true) for scan jobs, they still fail with OOME on large rows.
> The reason is that Scan field allowPartialResults is lost during job creation:
>   1. User creates a Job and sets a scan object via TableMapReduceUtil.initTableMapperJob(table_name, scanObj,...) -> which puts a result of TableMapReduceUtil.convertScanToString(scanObj) to the job config.
>   2. When the job starts - method TableInputFormat.setConfig retrieves a scan string from config and converts it to Scan object by calling TableMapReduceUtil.convertStringToScan - which results in a Scan object with a field allowPartialResults always set to false.
> I have tried to experiment and modify a TableInputFormat method setConfig() by forcing all scans to allow partial results and after this all jobs succeeded with no more OOME and I also noticed that mappers began to get partial results (Result.isPartial()).
> My use case is very simple - I just have large rows and expect a mapper to get them partially - to get same rowid several times with different key/value records.
> This would allow me not to worry about implementing my own result partitioning solution, which i would encounter in case the big amount of result key values could be transparently returned for a single large row.
> And from the other side - if a Scan object can return several records for the same rowid (partial results), perhaps the mapper should do the same.



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