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https://issues.apache.org/jira/browse/JENA-779?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andy Seaborne closed JENA-779.
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> Filter placement should be able to break up extend
> --------------------------------------------------
>
> Key: JENA-779
> URL: https://issues.apache.org/jira/browse/JENA-779
> Project: Apache Jena
> Issue Type: Improvement
> Components: ARQ, Optimizer
> Affects Versions: Jena 2.12.0
> Reporter: Rob Vesse
> Assignee: Andy Seaborne
> Fix For: Jena 2.12.1
>
> Attachments: JENA-779-filter-extend-extend,
> JENA-779-filter-extend_distinct.patch, JENA-779-single-extend.patch,
> JENA-779.patch
>
>
> The following query demonstrates a query plan seen internally which is
> considered sub-optimal.
> Consider the following query:
> {noformat}
> SELECT DISTINCT ?domainName
> {
> { ?uri ?p ?o }
> UNION
> {
> ?sub ?p ?uri
> FILTER(isIRI(?uri))
> }
> BIND(str(?uri) as ?s)
> FILTER(STRSTARTS(?s, "http://";))
> BIND(IRI(CONCAT("http://";, STRBEFORE(SUBSTR(?s,8), "/"))) AS ?domainName)
> }
> {noformat}
> Which ARQ optimises as follows:
> {noformat}
> (distinct
> (project (?domainName)
> (filter (strstarts ?s "http://";)
> (extend ((?s (str ?uri)) (?domainName (iri (concat "http://"; (strbefore
> (substr ?s 8) "/")))))
> (union
> (bgp (triple ?uri ?p ?o))
> (filter (isIRI ?uri)
> (bgp (triple ?sub ?p ?uri))))))))
> {noformat}
> Which makes the query engine do a lot of work because it computes the both
> the {{BIND}} expressions for lots of possible solutions that will then be
> rejected when for many of them it would only be necessary to compute the
> first simple {{BIND}} function.
> It would be better if the query was planned as follows:
> {noformat}
> (distinct
> (project (?domainName)
> (extend (?domainName (iri (concat "http://"; (strbefore (substr ?s 8)
> "/"))))
> (filter (strstarts ?s "http://";)
> (extend (?s (str ?uri))
> (union
> (bgp (triple ?uri ?p ?o))
> (filter (isIRI ?uri)
> (bgp (triple ?sub ?p ?uri)))))))))
> {noformat}
> Essentially when we try to push a filter through an {{extend}} if we
> determine that we cannot push it through the extend we should see if we can
> split the {{extend}} instead thus resulting in a partial pushing.
> Note that a user can re-write the original query to yield this plan if they
> make the second {{BIND}} a project expression like so:
> {noformat}
> SELECT DISTINCT (IRI(CONCAT("http://";, STRBEFORE(SUBSTR(?s,8), "/"))) AS
> ?domainName)
> {
> { ?uri ?p ?o }
> UNION
> {
> ?sub ?p ?uri
> FILTER(isIRI(?uri))
> }
> BIND(str(?uri) as ?s)
> FILTER(STRSTARTS(?s, "http://";))
> }
> {noformat}
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