[
https://issues.apache.org/jira/browse/JENA-1926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17147376#comment-17147376
]
Julian Gonggrijp commented on JENA-1926:
----------------------------------------
[~andy] So these particular two queries happen to be equivalent, although the
same could not be safely assumed about similar pairs of queries in general.
Point taken and thanks for confirming.
>From your explanation, I understand that the realized performance depends on
>many factors, only some of which are predictable across datasets and
>installations, and that it may be premature to document this particular
>situation for this reason. The somewhat spectacular performance difference
>between these particular two queries on my particular dataset and installation
>might be a statistical fluke. I will let this rest.
Thanks again for your patience and guidance, also to [~rvesse]. I wish you good
luck and perhaps we will meet again, here on Jira or maybe even in the Jena
codebase.
> Query execution speed depends more on WHERE clause order than expected
> ----------------------------------------------------------------------
>
> Key: JENA-1926
> URL: https://issues.apache.org/jira/browse/JENA-1926
> Project: Apache Jena
> Issue Type: Improvement
> Components: ARQ
> Affects Versions: Jena 3.15.0
> Reporter: Julian Gonggrijp
> Priority: Minor
>
> The following query takes about 6.5 seconds with my dataset, which
> unfortunately I cannot share. Note that {{?source}} is bound to a single IRI
> in all queries below; I'm leaving that out for brevity.
> {code:java}
> PREFIX oa: <http://www.w3.org/ns/oa#>
> PREFIX dcterms: <http://purl.org/dc/terms/>
> CONSTRUCT {
> ?annotation ?a ?b.
> ?body ?c ?d.
> ?target ?e ?f.
> ?selector ?g ?h.
> } WHERE {
> ?annotation oa:hasBody ?body;
> oa:hasTarget ?target;
> dcterms:creator ?user;
> ?a ?b.
> ?target oa:hasSource ?source;
> oa:hasSelector ?selector;
> ?e ?f.
> ?selector ?g ?h.
> OPTIONAL { ?body ?c ?d }.
> }
> {code}
> Compare this to the following query, which I believe is exactly equivalent
> but takes only 2 seconds:
> {code:java}
> CONSTRUCT {
> ?annotation ?a ?b.
> ?body ?c ?d.
> ?target ?e ?f.
> ?selector ?g ?h.
> } WHERE {
> ?annotation oa:hasBody ?body.
> OPTIONAL { ?body ?c ?d }.
> ?annotation oa:hasTarget ?target;
> dcterms:creator ?user;
> ?a ?b.
> ?target oa:hasSource ?source;
> oa:hasSelector ?selector;
> ?e ?f.
> ?selector ?g ?h.
> }
> {code}
> For comparison, leaving out the optional {{?body}} entirely, I get a query
> that executes in 1.7 seconds:
> {code:java}
> CONSTRUCT {
> ?annotation ?a ?b.
> ?target ?e ?f.
> ?selector ?g ?h.
> } WHERE {
> ?annotation oa:hasTarget ?target;
> dcterms:creator ?user;
> ?a ?b.
> ?target oa:hasSource ?source;
> oa:hasSelector ?selector;
> ?e ?f.
> ?selector ?g ?h.
> }
> {code}
> I'm a novice to SPARQL, but coming from SQL, I wouldn't expect query
> execution speed to depend so much on the order in which the criteria are
> given.
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
