Martin,
That's a complicated query and I haven't got my head aroud it completely
yet.
There are some useful points to understand:
A::
What is the time and outcome of these queries that focus on the main
data location part:
1/
SELECT (count(*) AS ?C) {
?paper iospress:publicationDate ?pubDate
FILTER(...date test...)
}
2/
SELECT (count(*) AS ?C) {
?paper iospress:publicationDate ?pubDate
iospress:publicationIncludesKeyword ?keyword .
FILETER (...date... && (regex (?keyword, "sickness", "i"))
3/
SELECT (count(*) AS ?C) {
{?paper rdf:type iospress:Chapter.}
union
{?paper rdf:type iospress:Article.}
?paper iospress:publicationDate ?pubDate
FILTER(...date test))
}
4/
SELECT (count(*) AS ?C) {
?paper iospress:publicationDate ?pubDate
FILTER(.. date test...)
{?paper rdf:type iospress:Chapter.}
union
{?paper rdf:type iospress:Article.}
}
B::
then is it the case that some optionals have more effect than others?
Some are "high risk":
---
OPTIONAL {
?author iospress:contributorAffiliation ?affiliation.
?affiliation rdfs:label ?university;
}
OPTIONAL {
?affiliation iospress:geocodingOutput ?geocoded.
?geocoded iospress-geocode:country ?country
}
---
Suppose the first does not match then the second is a lot of results
unrelated to ?paper.
C::
distinct
it might be worth trying without distinct because distinct can cause a
lot of results to be reduced to just a few, hiding redundant work.
Andy
On 18/05/2021 13:31, Martin Van Aken wrote:
Hello again,
After some more days of me trying to get a better performance & the
approval of my company, here is what we try to run (query at the bottom of
the mail).
For some context:
- This is a search for academia papers. Papers have multiple authors, and
authors are part of multiple universities. Papers also have multiple
keywords and are generally part of a set (an issue) itself part of a set (a
volume) itself part of a set (a journal).
- Our goal is to have a multicriteria search front end, so the query is
generated from a form with clauses selected by the user. The structure is
always the same, this example use a single condition on the "keyword"
- The set of data is relatively small - around 150k papers (so probably 1M
triples there), probably around 500k authors
- We use group/concat as we want to give as results one line per paper (vs
having one per paper per keyword for example)
- I've read OPTIONALS are pretty bad - but I've no real alternative here
that I know off when some fields can be present or not and I don't want to
throw away all that miss at least one
For our current results, all but the most precise queries (getting into a
super limited set of papers, like <10) get extremely slow (easily to dozens
of seconds, sometimes more). I feel that there is something obvious that
I'm missing, either in the query or my Jena config. The server is on an old
version but I make my tests locally on a 4.0.0 "out of the box" (0
configuration).
What I've tried:
- Removing the ORDER does not impact much
- Removing most optionals works... but remove the point of the query
- Using contains instead of regex does not impact much (I've the goal to
use Jena/Lucene integration for everything text related)
I'm really in for an opinion as taking my RDBMS background this is the
equivalent of less than 3M records split on around 8 tables - something
that should be queryable mostly in sub second times.
Any feedback is most welcome !
Martin
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX iospress: <http://ld.iospress.nl/rdf/ontology/>
PREFIX iospress-geocode: <http://ld.iospress.nl/rdf/geocode/>
PREFIX iospress-dt: <http://ld.iospress.nl/rdf/datatype/>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
SELECT ?type ?pubDate ?paper ?doi ?title ?abstract ?access
(group_concat(distinct ?authorName;separator=", ") as ?Authors)
(group_concat(distinct ?keyword;separator=", ") as ?keywords)
(group_concat(distinct ?university;separator=", ") as ?universities)
(group_concat(distinct ?country;separator=", ") as ?countries)
WHERE {
{?paper rdf:type iospress:Chapter.}
union
{?paper rdf:type iospress:Article.}
?paper rdfs:label ?title;
rdf:type ?type;
iospress:publicationDate ?pubDate;
iospress:publicationAbstract ?abstract;
iospress:publicationIncludesKeyword ?keyword;
iospress:publicationAuthorList [?idx ?author].
?issueOrBook iospress:partOf ?volumeOrSerie.
?paper iospress:partOf ?issueOrBook.
OPTIONAL {
?issueOrBook iospress:isbn ?bookIsbn.
}
OPTIONAL {
?paper iospress:publicationDoiUrl ?doi.
}
OPTIONAL {
?author rdfs:label ?authorName.
}
OPTIONAL {
?author iospress:contributorAffiliation ?affiliation.
?affiliation rdfs:label ?university;
}
OPTIONAL {
?affiliation iospress:geocodingOutput ?geocoded.
?geocoded iospress-geocode:country ?country
}
OPTIONAL {
?paper iospress:publicationAccessibility ?access.
}
OPTIONAL {
?volumeOrSerie iospress:partOf ?journal;
}
FILTER(
(
(datatype(?pubDate) = xsd:date && xsd:dateTime(?pubDate) >
"1999-12-31T23:00:00.000Z"^^xsd:dateTime && xsd:dateTime(?pubDate) <
"2021-05-18T12:16:58.841Z"^^xsd:dateTime ) ||
(datatype(?pubDate) = xsd:gYear && ?pubDate >=
"2000"^^xsd:gYear && ?pubDate <= "2021"^^xsd:gYear)
)
&& (regex (?keyword, "sickness", "i"))
)
}
GROUP BY ?type ?abstract ?pubDate ?paper ?doi ?title ?access
ORDER BY ?pubDate ?paper
LIMIT 50
On Thu, 6 May 2021 at 20:10, Andy Seaborne <a...@apache.org> wrote:
Hi there,
Showing the query would be helpful but some general remarks:
1/ If the query or the setup for Fuseki is needing more than the default
heap size, then it might be that the Java JVM is getting into a state of
heap exhaustion. This manifests as the CPU loading getting very high. It
will seem like nothing is happening (waiting for response).
2/ The query may be expensive.
Things to look for
* cross products - two parts of the query pattern that are not
connected.
{ ?s ?p ?o . ?a ?b ?c } is N-squared the size of the database.
* sort, spilling to disk or combined with a cross product the query.
3/ If no results are coming back, then the query is form that does not
stream back - sort, or CONSTRUCT maybe.
There was a useful presentation recently that talks about the principles
of query efficiency.
SPARQL Query Optimization with Pavel Klinov
https://www.youtube.com/watch?v=16eMswT2x2Y
More inline:
On 06/05/2021 09:54, Martin Van Aken wrote:
Hi!
I'm Martin, I'm a software developer new to the Triples/SPARQL world. I'm
currently building queries against a Fuseki/TDB backend (that I can work
on
too) and I'm getting into significant performance problems (including
never
ending queries).
Are updates also happening at the same time?
Despite what I thought was a good search on the apache
jena website I could not find a lot of insight about performance
investigation so I'm trying it here.
Most of my data experience comes from the relational world (ex: PG) so
I'm
sometimes drawing comparisons there.
To give some context my data set is around 15 linked concepts, with the
number of triples for each ranging from some hundreds to 500K - total
less
than 2 millions (documents/authors/publication kind of data).
Unto questions:
- When I'm facing a slow query, what are my investigation options. Is
there an equivalent of an "explain plan" in SQL pointing to the query
specific slow points? What's the advised way for performance checks
in
SPARQL?
qparse --print=opt --file query.rq
- Are there any performance setups to be aware of on the server side?
Like ways to check indexes are correctly built (outside of text
search that
I'm not working with for the moment)
- We're currently using TDB1. I've seen the transactional benefits of
TDB2 - are there performance improvements too that would warrant a
migration there ?
Not on the query side.
Andy
Thanks a lot already!
Martin
