[ https://issues.apache.org/jira/browse/PIG-2587?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13241007#comment-13241007 ] 

Bill Graham commented on PIG-2587:
----------------------------------

I agree if cosmetic changes happen to the script, all bets are off and you'll get a different signature.

Also agree about the 3 items out of scope here. The version of registered jars part would be ugly due to potential transitive dependancies changing and not being detected. 
                
> Compute LogicalPlan signature and store in job conf
> ---------------------------------------------------
>
>                 Key: PIG-2587
>                 URL: https://issues.apache.org/jira/browse/PIG-2587
>             Project: Pig
>          Issue Type: Improvement
>            Reporter: Bill Graham
>            Assignee: Bill Graham
>              Labels: 0.10_blocker
>             Fix For: 0.10, 0.11
>
>         Attachments: pig-2587_1.patch
>
>
> We'd like to be able to uniquely identify a re-executed script (possibly with different inputs/outputs) by creating a signature of the {{LogicalPlan}}. Here's the proposal:
> # Add a new method {{LogicalPlan.getSignature()}} that returns a hash of its {{LogicalPlanPrinter}} output.
> # In {{PigServer.execute()}} set the signature on the job conf after the LP is compiled, but before it's executed.
> (1) would allow an impl of {{PigProgressNotificationListener.setScriptPlan()}} to save the LP signature with the script metadata. Upon subsequent runs (2) would allow an impl of {{PigReducerEstimator}} (see PIG-2574) to retrieve the current LP signature and fetch the historical data for the script. It could then use the previous run data to better estimate the number of reducers.

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