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From "Robert Stupp (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7888) Decide the best way to define user-define functions
Date Sat, 13 Sep 2014 07:53:34 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7888?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14132595#comment-14132595
] 

Robert Stupp commented on CASSANDRA-7888:
-----------------------------------------

bq. I propose we just remove the UDF-as-classes
Can be simply optimized to use indy. I'm generally neutral on whether to keep or remove 'class'
UDFs regarding the implementation itself. But not having class UDFs can avoid potential deployment
issues.

bq. Still think we should be using invokedynamic
It's not necessary to do so because with CASSANDRA-7924 the code's refactored to generate
java-UDF classes that extend/implement {{UDFunction}} - so there's no more need to use either
reflection or indy during invocation.

> Decide the best way to define user-define functions
> ---------------------------------------------------
>
>                 Key: CASSANDRA-7888
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7888
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Benjamin Lerer
>              Labels: cql
>             Fix For: 3.0
>
>
> The goal of this ticket is to define what would be the best way from the ease of use
and performance point of view for defining User Defined Scalar Function and User Defined Aggregate
Function.
> I would like to clarify this point before we add support for User Defined Aggregate Function
as part of #4914 
> The current version of UDF is supporting only the addition of Scalar Function and does
so by allowing a User to provide some classes containing static methods that can then be loaded
as functions within Cassandra.
> The problem with the static method approach is that it force us internally to perform
a method call via reflection for each call of the function. So if the request load 10 000
rows the static method will be called 10 000 times via reflection.
> As the Method object is cached the HotSpot compiler will optimize the method call after
a certain amount of iterations. Nevertheless, from a performance point of view it is definetly
not a optimal situation.
> Ideally a proper solution from the performance point of view will limit the impact to
the function loading time (when the function is first added or at startup time) but not at
query time.
> The first solution to solve that problem would be to force the designer of a new function
to implements a specific interface like:
> {code}
> public interface UserDefinedScalarFunction
> {
>     Object execute(Object... args);
> }
> {code}
> or for aggregate function
> {code}
> public interface UserDefinedAggregateFunction
> {
>     UserDefinedAggregation newAggregate();
>     public interface UserDefinedAggregate 
>     {
>         void add(Object... args);
>         Object getResult();
>         void reset();
>     }
> } 
> {code} 
> This will allow use to create one object instance via reflection and then reuse that
object everytime the function is called.
> The problems with that approach is that we loose the type safety of the arguments and
of the return type and by consequence we will be able to detect a problem only at running
time.
> The second solution would be to force the designer of a new function to create a new
class in which it marks the method to execute with an annotation.
> {code}
> public class AbsFunction
> {
>     @Execute
>     public double abs(double d)
>     {
>         return Maths.abs(d);
>     }
> }
> {code}
> The same approach for aggregate functions will give:
> {code}
> public class AvgFunction
> {
>     private double sum;
>     private int count
>     @Add
>     public void addValue(double d)
>     {
>         sum += d;
> 	count++;
>     }
>     @Get
>     public double getAvg()
>     {
>         if (count == 0)
> 	    return 0;
>         return sum / count
>     }
>  
>     @Reset
>     public void clear()
>     {
> 	sum = 0;
>         count = 0;
>     }
> }
> {code}
> For this approach to work we need to use, at loading time, code generation for extending
the provided class with the method needed to adapt the class to our framework.
> The disavantage of it is that we will need to add a new library like javaassist to the
libraries used by C*.
> Its advantage is that it will allow us to detect type mismatch at creation time.



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