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From "Shubham Chopra (JIRA)" <j...@apache.org>
Subject [jira] Updated: (PIG-59) A new "ILLUSTRATE" command which will help people debug their pig programs
Date Thu, 10 Apr 2008 12:56:07 GMT

     [ https://issues.apache.org/jira/browse/PIG-59?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Shubham Chopra updated PIG-59:

    Attachment: exampleGenerator.patch

Patch for the latest trunk

> A new "ILLUSTRATE" command which will help people debug their pig programs
> --------------------------------------------------------------------------
>                 Key: PIG-59
>                 URL: https://issues.apache.org/jira/browse/PIG-59
>             Project: Pig
>          Issue Type: New Feature
>          Components: grunt
>            Reporter: Shubham Chopra
>         Attachments: exampleGenerator.patch, ExampleGenerator.patch
> I propose to add a new "ILLUSTRATE" command to Pig, which will help people debug their
Pig programs.
> The idea is to select a few example data items, and illustrate how they are transformed
by the sequence of Pig commands in the user's program. I have an algorithm that can select
an appropriate and concise set of example data items automatically. It does a better job than
random sampling would do; for example, random sampling suffers from the drawback that selective
operations such as filters or joins can eliminate *all* the sampled data items, giving you
empty results which is of no help in debugging.
> This "ILLUSTRATE" functionality will avoid people having to test their Pig programs on
large data sets, which has a long turnaround time and wastes system resources.
> Proposed Implementation:
> I will create a new package called org.apache.pig.exgen, which will contain the aforementioned
algorithm. The algorithm uses the "Local" execution operators (it does not run on hadoop),
so as to generate illustrative example data in near-real-time for the user. 
> For my algorithm to work properly, it needs to trace the "lineage" (sometimes called
"provenance") of data items as they flow through the local operator tree corresponding to
the user's Pig program. So I will have to add a "lineage tracer" to the Local operators, which
maintains a side data structure to represent the lineage, or derivation sequence, among data
items. The lineage tracer will be DISABLED BY DEFAULT, so it will not affect normal Pig operation.
> I will add a new method to PigServer called "PigServer.showExamples(LogicalPlan)", which
will cause my exgen algorithm to be invoked.
> I will also add a new command to Grunt, called ILLUSTRATE. Syntactically it will work
the same way as the STORE command. For example, a user might type:
> grunt> visits = load 'visits.txt' as (user, url, timestamp);
> grunt> recent_visits = filter visits by timestamp >= '20071201';
> grunt> user_visits = group recent_visits by user;
> grunt> num_user_visits = foreach user_visits generate group, COUNT(recent_visits);
> grunt> illustrate num_user_visits
> This would trigger my exgen algorithm, which will display something like:
> visits:
> (Amy, www.cnn.com, 20070218)
> (Fred, www.harvard.edu, 20071204)
> (Amy, www.bbc.com, 20071205)
> (Fred, www.stanford.edu, 20071206)
> recent_visits:
> (Fred, www.harvard.edu, 20071204)
> (Amy, www.bbc.com, 20071205)
> (Fred, www.stanford.edu, 20071206)
> user_visits:
> (Fred, { (Fred, www.harvard.edu, 20071204), (Fred, www.stanford.edu, 20071206) } )
> (Amy, { (Amy, www.bbc.com, 20071205) } )
> num_user_visits:
> (Fred, 2)
> (Amy, 1)

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