For these kind of performance issues it is useful to see the SPARQL algebra for the whole query, not just fragments of the query. You can use the qparse command for the version of Jena you are using to see how it is optimising your queries e.g.
qparse --explain --query example.rq As Lorenz suggests this may be the optimiser making a bad guess at the appropriate order in which to evaluate the triple patterns within the BGP but without the larger query context or the algebra all we can do is guess. Rob From: Mikael Pesonen <[email protected]> Date: Tuesday, 1 November 2022 at 12:53 To: [email protected] <[email protected]> Subject: Re: Weird sparql problem Diferent case, but again hanging makes no sense to user, whatever are the technical reasons. VALUES ?sct_code { "298314008" } ?c skosxl:prefLabel [ lsu:code ?sct_code ] returns one row immediately, but VALUES ?sct_code { "298314008" } ?c skosxl:prefLabel [ lsu:code ?sct_code ]; skos:inScheme lsu:SNOMEDCT_US hangs forever skos:inScheme lsu:SNOMEDCT_US; On 18/10/2022 9.08, Lorenz Buehmann wrote: > Hi, > > comments inline > > On 17.10.22 14:35, Mikael Pesonen wrote: >> This works as a separate query, but not in a the middle, since ?s >> gets new values instead of binding to previous ?s. >> >> { select ?t where { >> ?s a ?t . >> } limit 10} >> ?t skos:prefLabel ?l > > > In the middle of what? Subqueries will be evaluated first - if you > really want labels for classes, you should use a DISTINCT in the > subquery such that the intermediate result is small, there shouldn't > be that many classes, but many instances with the same class, thus, > the join would be more expensive than necessary. > > >> >> On 17/10/2022 14.56, Mikael Pesonen wrote: >>> >>> ?s a ?t . >>> ?t skos:prefLabel ?l >>> >>> returns 3 million triples. Maybe it's related to this? > > I don't see how this should be related to your initial query where ?s > was bound, which in my opinion should be an easy join. Is it possible > for you to share the dataset somehow? Also, what you can do is to > compute statistics for the TDB database with tdbstats tool [1] from > commandline and put it into the TDB folder. But even without the query > plan should take the first triple pattern, use the spo index as s and > p are bound, then pass the bindings of ?o to the evaluation of the > second triple pattern > > [1] > https://jena.apache.org/documentation/tdb/optimizer.html#generating-a-statistics-file > > >>> >>> >>> On 21/09/2022 9.15, Lorenz Buehmann wrote: >>>> Weird, only 10M triples and each triple pattern returns only 1 >>>> binding, thus, the size is tiny - honestly I can't think of >>>> anything except for open connections, but as you mentioned, running >>>> the queries with only one triple pattern works as expected, so that >>>> too many open connections shouldn't be an issue most likely. >>>> >>>> Can you reproduce this behavior with newer Jena versions like 4.6.1? >>>> >>>> Or can you reproduce this on different servers as well? >>>> >>>> Is it also stuck of your run the query directly after you restart >>>> Fuseki? >>>> >>>> >>>> On 19.09.22 13:49, Mikael Pesonen wrote: >>>>> >>>>> >>>>> On 15/09/2022 17.48, Lorenz Buehmann wrote: >>>>>> Forgot: >>>>>> >>>>>> - size of result for each triple pattern? Might affect if hash >>>>>> join can be used. >>>>> It's one row for each. >>>>>> >>>>>> - your hardware? >>>>> Normal server with 16gigs mem. >>>>>> >>>>>> - is it just the first query after starting Fuseki? Connections >>>>>> have been closed? Note, there was also a bug in a recent Jena >>>>>> version, but only with TDB and too many open connections. It has >>>>>> been resolved with release 4.6.1. >>>>> Jena has been running quite a while. >>>>>> >>>>>> Might not be related, but I'm mentioning all things here >>>>>> nevertheless. >>>>>> >>>>>> >>>>>> On 15.09.22 11:16, Mikael Pesonen wrote: >>>>>>> >>>>>>> This returns one row fast, say :C1 >>>>>>> >>>>>>> SELECT * >>>>>>> FROM <https://a.b.c> >>>>>>> WHERE { >>>>>>> <https://x.y.z> a ?t . >>>>>>> #?t skos:prefLabel ?l >>>>>>> } >>>>>>> >>>>>>> >>>>>>> and this too: >>>>>>> >>>>>>> SELECT * >>>>>>> FROM <https://a.b.c> >>>>>>> WHERE { >>>>>>> #<https://x.y.z> a ?t . >>>>>>> :C1 skos:prefLabel ?l >>>>>>> } >>>>>>> >>>>>>> >>>>>>> But this always hangs until timeout >>>>>>> >>>>>>> SELECT * >>>>>>> FROM <https://a.b.c> >>>>>>> WHERE { >>>>>>> <https://x.y.z> a ?t . >>>>>>> ?t skos:prefLabel ?l >>>>>>> } >>>>>>> >>>>>>> What am I missing here? I'm using Fuseki web GUI. Thanks! >>>>> >>> >> -- Lingsoft - 30 years of Leading Language Management www.lingsoft.fi<http://www.lingsoft.fi> Speech Applications - Language Management - Translation - Reader's and Writer's Tools - Text Tools - E-books and M-books Mikael Pesonen System Engineer e-mail: [email protected] Tel. +358 2 279 3300 Time zone: GMT+2 Helsinki Office Eteläranta 10 FI-00130 Helsinki FINLAND Turku Office Kauppiaskatu 5 A FI-20100 Turku FINLAND
