Julian Gonggrijp created JENA-1926:
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Summary: 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: Fuseki, TDB2
Affects Versions: Jena 3.15.0
Reporter: Julian Gonggrijp
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.
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