Virtuoso Open-Source Edition

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    • Working with SPARQL endpoint constraints via LIMIT & OFFSET

    The DBpedia SPARQL endpoint is configured with the following Virtuoso INI setting:

    MaxSortedTopRows = 40000

    This setting sets a threshold on sorted rows. SPARQL queries that include OFFSET and LIMIT will feel the effect of the hard limit set in the INI. For instance, this query --

      DEFINE  sql:big-data-const 0 
  SELECT  DISTINCT  ?p 
                    ?s
    FROM <http://dbpedia.org>
   WHERE
     { 
       ?s  ?p  <http://dbpedia.org/resource/Germany> 
     }
ORDER BY  ASC(?p)
  OFFSET  40000
   LIMIT  1000

    -- will return the following error on execution --

    HttpException: 500 SPARQL Request Failed

Virtuoso 22023 Error SR353: Sorted TOP clause specifies more then 41000 rows to sort. 
Only 40000 are allowed. 
Either decrease the offset and/or row count or use a scrollable cursor

    To prevent this error, you can leverage the use of subqueries which make better use of temporary storage. For example --

    SELECT  ?p 
        ?s 
 WHERE 
   {
     {
         SELECT  DISTINCT  ?p 
                           ?s 
           FROM  <http://dbpedia.org> 
          WHERE   
             { 
               ?s  ?p  <http://dbpedia.org/resource/Germany> 
             } 
       ORDER BY ASC(?p) 
     }
   } 
OFFSET 50000 
 LIMIT 1000

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