[jira] [Commented] (PIG-3642) Direct HDFS access for small jobs (fetch)

["Lorand Bendig (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PIG-3642?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13889824#comment-13889824 ] 

Lorand Bendig commented on PIG-3642:
------------------------------------

[~cheolsoo], great! Thank you for your assistance! I'll take care of the docs.

> Direct HDFS access for small jobs (fetch) 
> ------------------------------------------
>
>                 Key: PIG-3642
>                 URL: https://issues.apache.org/jira/browse/PIG-3642
>             Project: Pig
>          Issue Type: Improvement
>            Reporter: Lorand Bendig
>            Assignee: Lorand Bendig
>             Fix For: 0.13.0
>
>         Attachments: PIG-3642-3.patch, PIG-3642-4.patch, PIG-3642-5.patch, PIG-3642-6.patch, PIG-3642.patch
>
>
> With this patch I'd like to add the possibility to directly read data from HDFS instead of launching MR jobs in case of simple (map-only) tasks. Hive already has this feature (fetch). This patch shares some similarities with the local mode of Pig 0.6. Here, fetching kicks off when the following holds for a script:
> * it contains only LIMIT, FILTER, UNION (if no split is generated), STREAM, (nested) FOREACH with expression operators, custom UDFs..etc
> * no scalar aliases
> * no SampleLoader
> * single leaf job
> * DUMP (no STORE)
> The feature is enabled by default and can be toggled with:
> * -N or -no_fetch 
> * set opt.fetch true/false; 
> There's no STORE support because I wanted to make it explicit that this "optimization" is for launching small/simple scripts during development, rather than querying and filtering large number of rows on the client machine. However, a threshold could be given on the input size (an estimation) to determine whether to prefer fetch over MR jobs, similar to what Hive's '{{hive.fetch.task.conversion.threshold}}' does. (through Pig's LoadMetadata#getStatistic ?)



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