[jira] [Commented] (JENA-780) Single use extend expressions could be substituted directly for their later usage

["ASF subversion and git services (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/JENA-780?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14615116#comment-14615116 ] 

ASF subversion and git services commented on JENA-780:
------------------------------------------------------

Commit bdcf8a6056092b04bf644607b6176afd0e834544 in jena's branch refs/heads/eliminate-assignments from [~rvesse]
[ https://git-wip-us.apache.org/repos/asf?p=jena.git;h=bdcf8a6 ]

Further work on eliminating/inlining assignments (JENA-780)

- Support elimination/inlining to OpGroup and OpTopN
- Only eliminate/inline when expressions are stable
- Only inline into sort conditions if the expression is constant
- Expand test coverage


> Single use extend expressions could be substituted directly for their later usage
> ---------------------------------------------------------------------------------
>
>                 Key: JENA-780
>                 URL: https://issues.apache.org/jira/browse/JENA-780
>             Project: Apache Jena
>          Issue Type: Improvement
>          Components: ARQ, Optimizer
>    Affects Versions: Jena 2.12.0
>            Reporter: Rob Vesse
>            Assignee: Rob Vesse
>            Priority: Minor
>         Attachments: JENA-780.patch
>
>
> This RFE is a follow on from JENA-779, the query with a sub-optimal plan there uses a {{BIND}} to create a value which is then only used once in a subsequent filter.
> Actually that query uses it twice but I think the general approach I am trying to describe in this RFE bears consideration.  In this case it seems like it would be possible to substitute the extend expression for the bound variable in the filter expression.
> Simplified variant of original query such that the bound value is only used once:
> {noformat}
> SELECT DISTINCT ?uri
> {
>   { ?uri ?p ?o }
>   UNION
>   {
>     ?sub ?p ?uri
>     FILTER(isIRI(?uri))
>   }
>   BIND(str(?uri) as ?s)
>   FILTER(STRSTARTS(?s, "http://"))
> }
> {noformat}
> Rewritten query:
> {noformat}
> SELECT DISTINCT ?domainName
> {
>   { ?uri ?p ?o }
>   UNION
>   {
>     ?sub ?p ?uri
>     FILTER(isIRI(?uri))
>   }
>   FILTER(STRSTARTS(str(?uri), "http://"))
> }
> {noformat}
> Which avoids an extend expression whose value is only used once and will ultimately be thrown away.
> From a {{Transform}} standpoint this is likely awkward to implement in a pure transform since it requires knowledge about the query structure above the {{FILTER}} i.e. whether the bound variable is used elsewhere and so would need to use before and after visitors to track that additional state but I think this is a feasible optimisation.



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