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From "Ashutosh Chauhan (JIRA)" <j...@apache.org>
Subject [jira] Updated: (PIG-820) PERFORMANCE: The RandomSampleLoader should be changed to allow it subsume another loader
Date Sat, 20 Jun 2009 23:56:07 GMT

     [ https://issues.apache.org/jira/browse/PIG-820?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Ashutosh Chauhan updated PIG-820:
---------------------------------

    Attachment: pig-820.patch

In addition to explanation above SampleOptimizer is introduced which visits the compiled MR
plan to detect this pattern (MR operator containing only load-store followed by MR operator
containing sampling job in map plan). If this pattern is present, SampleOptimizer deletes
the unnecessary predecessor MR operator and replaces the POLoad of sampling job with RandomSampleLoader
which uses the loader of its predecessor. 

> PERFORMANCE:  The RandomSampleLoader should be changed to allow it subsume another loader
> -----------------------------------------------------------------------------------------
>
>                 Key: PIG-820
>                 URL: https://issues.apache.org/jira/browse/PIG-820
>             Project: Pig
>          Issue Type: Improvement
>          Components: impl
>    Affects Versions: 0.3.0
>            Reporter: Alan Gates
>            Assignee: Alan Gates
>         Attachments: pig-820.patch
>
>
> Currently a sampling job requires that data already be stored in BinaryStorage format,
since RandomSampleLoader extends BinaryStorage.  For order by this
> has mostly been acceptable, because users tend to use order by at the end of their script
where other MR jobs have already operated on the data and thus it
> is already being stored in BinaryStorage.  For pig scripts that just did an order by,
an entire MR job is required to read the data and write it out
> in BinaryStorage format.
> As we begin work on join algorithms that will require sampling, this requirement to read
the entire input and write it back out will not be acceptable.
> Join is often the first operation of a script, and thus is much more likely to trigger
this useless up front translation job.
> Instead RandomSampleLoader can be changed to subsume an existing loader, using the user
specified loader to read the tuples while handling the skipping
> between tuples itself.  This will require the subsumed loader to implement a Samplable
Interface, that will look something like:
> {code}
> public interface SamplableLoader extends LoadFunc {
>     
>     /**
>      * Skip ahead in the input stream.
>      * @param n number of bytes to skip
>      * @return number of bytes actually skipped.  The return semantics are
>      * exactly the same as {@link java.io.InpuStream#skip(long)}
>      */
>     public long skip(long n) throws IOException;
>     
>     /**
>      * Get the current position in the stream.
>      * @return position in the stream.
>      */
>     public long getPosition() throws IOException;
> }
> {code}
> The MRCompiler would then check if the loader being used to load data implemented the
SamplableLoader interface.  If so, rather than create an initial MR
> job to do the translation it would create the sampling job, having RandomSampleLoader
use the user specified loader.

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