Re: Query Performance Degrade With Sorting In Subquery

[Rob @ DNR]

This is due to Jena’s lazy evaluation in its query engine.

When you include a LIMIT clause on its own Jena only needs find the first N 
results (10 in your example) at which point it can abort any further processing 
and return results.  In this case evaluation is lazy.

When you include LIMIT and ORDER BY clauses Jena has to find all possible 
results, sort them, and then return only the first N results.  In this case 
full evaluation is required.

One possible approach might be to split into multiple queries i.e. do one query 
to get your main set of results, and then separately issue the related item 
sub-queries with concrete values substituted into for your ?concept and 
?titleSkosXl values as while Jena will still need to do full evaluation 
injecting a concrete value will constrain the query evaluation further

Hope this helps,

Rob

From: Chirag Ratra <chirag.ra...@bold.com>
Date: Tuesday, 19 March 2024 at 07:46
To: users@jena.apache.org <users@jena.apache.org>
Subject: Query Performance Degrade With Sorting In Subquery
Hi,

Facing a big performance degradation  while using sort query in subquery
If I run query without sorting the response of my query is around 200 ms
but when I use the order by query,  performance comes to be around 4-5
seconds.

Here is my query :

PREFIX text: <http://jena.apache.org/text#<http://jena.apache.org/text>>
PREFIX skos: 
<http://www.w3.org/2004/02/skos/core#<http://www.w3.org/2004/02/skos/core>>
PREFIX skosxl: 
<http://www.w3.org/2008/05/skos-xl#<http://www.w3.org/2008/05/skos-xl>>
PREFIX relations: 
<https://cxdata.bold.com/ontologies/myDomain#<https://cxdata.bold.com/ontologies/myDomain>>

SELECT ?concept ?titleSkosxl ?title ?languageCode (GROUP_CONCAT(DISTINCT
?relatedTitle; separator=", ") AS ?relatedTitles) (GROUP_CONCAT(DISTINCT
?alternate; separator=", ") AS ?alternates)
WHERE
{
  (?titleSkosxl ?score) text:query ('cashier').

?concept skosxl:prefLabel ?titleSkosxl.
  ?titleSkosxl skosxl:literalForm ?title.
  ?titleSkosxl relations:usedInLocale ?controlledList.
  ?controlledList relations:languageMarketCode ?languageCode
FILTER(?languageCode = 'en-US').


#  get alternate title
OPTIONAL
  {
        Select ?alternate  {
        ?concept skosxl:altLabel ?alternateSkosxl.
        ?alternateSkosxl skosxl:literalForm ?alternate;
  relations:hasUserCount ?alternateUserCount.
        }
ORDER BY DESC (?alternateUserCount) LIMIT 10
}

#  get related titles
  OPTIONAL
  {
      Select ?relatedTitle
      {
            ?titleSkosxl relations:isRelatedTo ?relatedSkosxl.
            ?relatedSkosxl skosxl:literalForm ?relatedTitle;
            relations:hasUserCount ?relatedUserCount.
      }
ORDER BY DESC (?relatedUserCount) LIMIT 10
   }
}
GROUP BY ?concept ?titleSkosxl ?title ?languageCode ?alternateJobTitle
?notation
ORDER BY DESC(?jobtitleWeight) DESC(?score)
LIMIT 10

The sorting queries given causes huge performance degradation :
ORDER BY DESC (?alternateUserCount) AND ORDER BY DESC (?relatedUserCount)

How can this be improved, this sorting will be used in each and every query
in my application.

--








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