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https://issues.apache.org/jira/browse/PIG-820?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ashutosh Chauhan updated PIG-820:
---------------------------------
Status: Open (was: Patch Available)
Missed test files.
> 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, 0.4.0
> Reporter: Alan Gates
> Assignee: Ashutosh Chauhan
> Fix For: 0.4.0
>
> Attachments: pig-820.patch, pig-820_v2.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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