Public SPARQL Endpoint
This site describes basic configuration parameters and important usage notes or limitations regarding the public DBpedia SPARQL Endpoint query service. The information on this side only applies for the English DBpedia SPARQL endpoint. For information about the endpoints of individual chapters see the website of the according chapter.
Backend and frontend type
The SPARQL backend is powered by Virtuoso and hosted by OpenLink Software.
The frontend uses nginx to cache request for a query string (???)
Rates and Limitations
In terms of a Fair Use Policy and to provide a stable and responsive endpoint for the community, there is a limit on the number of connections/sec you can make, as well as restrictions on resultsets and query time, as per the following settings:
ResultSetMaxRows = 2000 MaxQueryExecutionTime = 120 (seconds) MaxQueryCostEstimationTime = 1500 (seconds) maximum connections per sec = ???
NOTE: Queries which timed out, will return NO error status code BUT will return PARTIAL results in a best effort fashion. This is realized by Virtuoso's antytime queries feature which is enabled for the public endpoint. See the designated subsection for more details.
Partial Results for timed-out queries (AntytimeQueries)
The public endpoint features Virtuoso's antytime queries to return partial results for timed-out queries. See http://docs.openlinksw.com/virtuoso/anytimequeries/ for a detailled explanation.
ATTENTION: Timed-out queries will return partial results the same way as completed queries (NO error HTTP status code will sent BUT a 200 OK code).
NOTE: For queries with aggregates this implies that the returned aggregated values are not correct with respect to the whole DBpedia dataset and can vary between query executions!!!
In order to check whether a query delivered partial results, an applications needs to evaluate HTTP return headers. If results are impacted by the anytime query feature this will be indicated by the following HTTP headers in the query response:
X-SQL-State: S1TAT X-SQL-Message: RC...: Returning incomplete results, query interrupted by result timeout. Activity: 2.295M rnd 10.05M seq [...]
The public endpoint for the English chapter does NOT include all available DBpedia data sets. The following datasets are loaded (Release 2016-10)
Furthermore you can read this post how to deal with restrictions on the public DBpedia endpoint.