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https://issues.apache.org/jira/browse/PIG-1613?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Olga Natkovich updated PIG-1613:
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Release Note:
I think this should go into Advanced Topics in the UDF manual
There are multiple ways for a UDF to be invoked. The simplest UDF can just
extend EvalFunc that requires only exec function to be implemented as described
in the How to Write a Simple Eval Function section. Every eval UDF must
implement this. Additionally, if a function is algebraic, it can implement
Algebraic interface to significantly improve query performance in the cases
when combiner can be used. The Aggregate Functions section covers this topic in
detail. Finally, a function that can process tuples in the incremental fashion
can also implement Accumulator interface to improve query memory consumption.
Accumulator interface section explains this interface.
The exact method by which UDF is invoked is selected by the optimizer based on
the UDF type and the query. Note that only a single interface is used at any
given time. The optimizer tries to find the most efficient way to execute the
function. If a combiner is used and function implements Algebraic interface
then this interface will be used to invoke the function. If the combiner is not
invoked but accumulator can be used and the function implements Accumulator
interface then that interface is used. If neither of the conditions is
satisfied then exec function is used to invoke the UDF.
Can one of the developers review the release notes to make sure they are
accurate, thanks.
> Explain how different UDF interfaces are used
> ---------------------------------------------
>
> Key: PIG-1613
> URL: https://issues.apache.org/jira/browse/PIG-1613
> Project: Pig
> Issue Type: Improvement
> Components: documentation
> Affects Versions: 0.7.0
> Reporter: Olga Natkovich
> Assignee: Corinne Chandel
> Fix For: 0.8.0
>
>
> The current documentation describes individual UDF interfaces such as
> Algebraic and Accumulator but not their precedence or how they interact with
> each other and why you might want to implement several of them.
> Corrine, I will add release notes to this JIRA shortly. Don't worry about it
> till then.
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