Scott, thank you so much for your advice! I will try to optimize my queries, but I'm also eager for more performance tuning hints.
Cheers, Christian On 28 Mai, 20:51, Scott Henninger <[email protected]> wrote: > Christian; In the end it's really no different than any kind of > database application. There will always be a point in > whichperformancesuffers and/or memory becomes scarce. There are also > tradeoffs for large heap spaces - garbage collection overhead > increases with the size of memory you are trying collect garbage on. > > So the first set of advice I'd give is to look carefully at your > queries. Keep in mind that ?s ?p ?o says "bring everything into > memory", thus defeating the purpose of using a back-end. Fortunately > Composer's SPARQL engine, ARQ, tends to ignore these. But the advice > is still sage - cut down the size of the graph match as soon as > possible. Note that OPTIONAL is fairly dangerous to start with - it > states "find this graph pattern or that graph pattern" and thus > increases the search space. We are working to optimize this better. > > Turn on Profiling Mode in the SPARQL View's query debugger and find > the triple pattern placements that result in the fewest match attempts > - i.e. use it to make sure you prune the search space optimally. It > will also give you the true ordering of evaluation, which is normally > top-to-bottom, but ARQ will perform some optimizations. Try turning > on filter placement and filter early, if that's possible. Use LIMIT > and OFFSET to experiment with pieces of the results. > > Avoid string matches as much as possible - FILTERs are often deadly in > this respect, so make sure you cut down your search space as much as > possible before doing this kind of string compare. Note this nearly > conflicts with the earlier statement. Where to place filters depends > on how computationally expensive the filter expression is and how much > it prunes the search space for downstream processing. > > There are probably a few other SPARQL query tips and I'd love to hear > from others on this. (Self-plug alert: We cover SPARQL queryperformanceour > Advanced Product training.) > > Divide-and-conquer is the next step. View your data back-end as a > huge well and you only want a specific bucketful at a time, being > careful to leave the rest where it is. I.e. view heap space memory as > a limited resource. SPARQLMotion is an excellent tool for this task > as it can be used to get specific sets of triples that can be combined > for further processing. Remember that ASK queries terminate when a > match is found, so if you just need to find if the graph pattern > exists, ASK is much more efficient than SELECT. > > For SPIN the advice is pretty much the same (Holger can say more). Be > sure to use ?this because the engine is optimized for that pre-bound > variable. SPIN will iterate until no new triples are found unless you > tell the engine otherwise. Turn iterations off if that makes sense > for your application. If some rules don't have value in forward- > chaining, set the rule property's spin:rulePropertyMaxIterationCount > to the maximum needed. > > Many things to try here and I hope this isn't mistaken as being the > last word on this topic! > > -- Scott > > On May 28, 12:36 pm, Christian Fuerber <[email protected]> wrote: > > > Hi Holger, > > > thank you for the information. I finally set up a TDB triplestore with > > over 53 Mio triples and it shows up perfectly in TBC. But now I'm > > havingperformanceproblems when running SPARQL queries over the > > triplestore in TBC's SPARQL view. SPIN constraints also seem to run > > forever. I'm using the 64bit version of TBC 3.3.1 SE and set the java > > heapspace limit to 6144m. > > > Is there any configurations the can speed up TBC's queries and SPIN > > constraints besides query optimization and java heapspace settings? > > > Thanks, > > Christian > > > On 24 Mai, 03:51, Holger Knublauch <[email protected]> wrote: > > > > Hi Christian, > > > > TopBraid's Sesame 2 integration is not as optimized as our other database > > > interfaces. In practice this means that TBC cannot use any native > > > optimizations that the database server (in your case Virtuoso) may > > > provide. Instead, it will break down even the most complex SPARQL queries > > > into small findSPO queries, which may lead to > > > significantperformanceproblems. Maybe that's why constraint checking > > > apparently did not work for you when you can SPIN constraints on > > > Virtuoso. With smaller databases this impact may not have been > > > sufficiently severe to notice. But I am glad that you have been able to > > > confirm that Virtuoso is working well with TBC in principle. > > > > Over the week end we also had some enlightening examples of SPARQL > > > queries that were not optimized: we had a query with three OPTIONAL > > > clauses, leading to a large number of potential combinations. Replacing > > > those with other SPARQL patterns were leading to many orders of magnitude > > > speed improvements. Just saying this in case you have some "dangerous" > > > queries in your constraints. I assume you have executed the queries > > > individually, e.g. from the SPARQL view, to test theirperformancebefore > > > putting them into your SPIN constraint library. > > > > Finally, I discovered aperformanceissue after running the SPIN > > > constraints from the Problems View: if hundreds or thousands of > > > violations were found, then just updating those into the Problems view > > > may freeze the system. I have just fixed this for 3.3.2 (and 3.4). > > > > Regards, > > > Holger > > > > On May 21, 2010, at 10:25 PM, Christian Fuerber wrote: > > > > > Hi Holger, > > > > > fortunately i can apply SPIN constraints now on the small graph (245 > > > > triples) in virtuoso. Although I still do not know what the problem > > > > was. Maybe. it works now because I reinstalled java. I will also send > > > > you the error log, in case you are interested. > > > > > Thanks a lot, > > > > > Christian > > > > > On 21 Mai, 00:20, Holger Knublauch <[email protected]> wrote: > > > >> On May 21, 2010, at 1:08 AM, Christian Fuerber wrote: > > > > >>> Hi Holger, > > > > >>> thank you for the quick response. Yes, I could successfully connect to > > > >>> a graph in virtuoso that has 245 triples. But the SPIN constraint > > > >>> checks are not working on the graph's data. I receive an error "Could > > > >>> not run checker" when executing "Refresh and show problems > > > >>> (constraints)". SPARQL in TBC is also not working. I just can see the > > > >>> classes and instances in the editor. > > > > >> Are there any more details available, e.g. the Error Log? > > > > >> And yes, TDB will almost certainly be faster for SPARQL, because it > > > >> will "live" in the same JVM, so no communication overhead is needed. > > > >> Furthermore, TDB is better optimized to work with the ARQ SPARQL > > > >> engine. > > > > >> Thanks > > > >> Holger > > > > >> -- > > > >> You received this message because you are subscribed to the Google > > > >> Group "TopBraid Suite Users", the topics of which include TopBraid > > > >> Composer, > > > >> TopBraid Live, TopBraid Ensemble, SPARQLMotion and SPIN. > > > >> To post to this group, send email to > > > >> [email protected] > > > >> To unsubscribe from this group, send email to > > > >> [email protected] > > > >> For more options, visit this group > > > >> athttp://groups.google.com/group/topbraid-users?hl=en > > > > > -- > > > > You received this message because you are subscribed to the Google > > > > Group "TopBraid Suite Users", the topics of which include TopBraid > > > > Composer, > > > > TopBraid Live, TopBraid Ensemble, SPARQLMotion and SPIN. > > > > To post to this group, send email to > > > > [email protected] > > > > To unsubscribe from this group, send email to > > > > [email protected] > > > > For more options, visit this group at > > > >http://groups.google.com/group/topbraid-users?hl=en > > > > -- > > > You received this message because you are subscribed to the Google > > > Group "TopBraid Suite Users", the topics of which include TopBraid > > > Composer, > > > TopBraid Live, TopBraid Ensemble, SPARQLMotion and SPIN. > > > To post to this group, send email to > > > [email protected] > > > To unsubscribe from this group, send email to > > > [email protected] > > > For more options, visit this group > > > athttp://groups.google.com/group/topbraid-users?hl=en -- You received this message because you are subscribed to the Google Group "TopBraid Suite Users", the topics of which include TopBraid Composer, TopBraid Live, TopBraid Ensemble, SPARQLMotion and SPIN. 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