[jira] [Commented] (JENA-630) Do constant folding as part of query optimisation

[Andy Seaborne (JIRA)]

    [ 
https://issues.apache.org/jira/browse/JENA-630?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13964410#comment-13964410
 ] 

Andy Seaborne commented on JENA-630:
------------------------------------

It looks better when folding occurs.

I then tried a non-folding expression:
{noformat}
        Expr expr = SSE.parseExpr("(* ?y (+ (* ?x 4) (* ?z 6 )))") ;
        Expr expr2 = ExprTransformer.transform(new ExprTransformConstantFold(), 
expr) ;
        System.out.println("==> "+expr2) ;
        System.out.println("DONE") ;
{noformat}
and got:
{noformat}
ExprFunction2: ( ?x * 4 )
ExprVar: ?x
NodeValue: 4
ExprFunction2: ( ?z * 6 )
ExprVar: ?z
NodeValue: 6
ExprFunction2: ( ( ?x * 4 ) + ( ?z * 6 ) )
ExprFunction2: ( ?x * 4 )
ExprVar: ?x
NodeValue: 4
ExprFunction2: ( ?z * 6 )
ExprVar: ?z
NodeValue: 6
ExprFunction2: ( ?y * ( ( ?x * 4 ) + ( ?z * 6 ) ) )
ExprVar: ?y
ExprFunction2: ( ( ?x * 4 ) + ( ?z * 6 ) )
ExprFunction2: ( ?x * 4 )
ExprVar: ?x
NodeValue: 4
ExprFunction2: ( ?z * 6 )
ExprVar: ?z
NodeValue: 6
==> ( ?y * ( ( ?x * 4 ) + ( ?z * 6 ) ) )
DONE
{noformat}

{{copySubstitute}} on the top node gets called and it recursively calls 
copySubstitute on subnodes.  But these have been processed.

It's the call to {{copySubstitute}} in 
{{ExprTransformConstantFold.transform(ExprFunction2 func, Expr expr1, Expr 
expr2)}} - the process does not need to copy at this point.

I've attached a possible  {{ExprTransformConstantFold}} and a test programme -- 
a couple of things need cleaning up for a real version 
({{ExprFunctionN.eval(List<NodeValue>}} needs to be public but that has knock 
on changes which are not issues for this discussion; I hit the 
ARQInternalErrorException from TestUSerFuntionsInSparql but looks like a 
separate matter).

This does not make this issue "major" -- the optimization is almost certainly 
beneficial.

> Do constant folding as part of query optimisation
> -------------------------------------------------
>
>                 Key: JENA-630
>                 URL: https://issues.apache.org/jira/browse/JENA-630
>             Project: Apache Jena
>          Issue Type: Improvement
>          Components: ARQ
>    Affects Versions: Jena 2.11.1
>            Reporter: Rob Vesse
>            Assignee: Rob Vesse
>             Fix For: Jena 2.11.2
>
>
> Currently Jena does not automatically simplify expressions by constant 
> folding even though the function API actually has support for this already 
> baked into it.
> This issue will track work to integrate a transform for this into the 
> standard optimiser.



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