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Am 17.02.2016 um 09:54 schrieb Katie Filbert: > On Wed, Feb 17, 2016 at 9:39 AM, Markus Krötzsch > <[email protected] > <mailto:[email protected]>> wrote: > > On 17.02.2016 08:16, Stas Malyshev wrote: > > Hi! > > (2) Shouldn't BlazeGraph do the caching (too)? It knows how much a > query costs to re-run and it could even know if a query is affected > by a data > > > BlazeGraph does a lot of caching, but it's limited by the memory > and it AFAIK does not do whole query caching (like mysql does, for > example) - which means if you run two big queries one after > another, the latter could remove from cache what the former put > there. Its caching, AFAIK, is on much lower level. Which is helpful > too since different queries share a lot of underlying data, but not > exactly our case here. > > update (a cache might still be the same as a current result even > after many data changes). Having several caching layers is useful, > but the more elaborate (query-structure dependent) caching > strategies should maybe be left to the database. > > > I don't think Blazegraph does anything like resolving changes to > see if query results changed, that sound like pretty hard thing to > do in triple store. You can manually store specific query result > AFAIK but that's just form of writing data as I understand and may > not be very scalable. > > > Yes, in general this would be extremely hard. There are some easy > cases one could catch, but it is not clear how effective this > would be for our load. I am just saying we should not try to build > a query-aware caching strategy that would better be done on a lower > level. > > > The points (3)-(5) are based on guessing. As Magnus said, some > analysis could help to confirm or refute this. On the other hand, > caching should not just focus on current usage patterns only, but > consider a bit what could happen in the future. > > > Well, again the problem is that one use case that I think > absolutely needs caching - namely, exporting data to graphs, maps, > etc. deployed on wiki pages - is also the one not implemented yet > because we don't have cache (not only, but one of the things we > need) so we've got chicken and egg problem here :) Of course, we > can just choose something now based on educated guess and change it > later if it works badly. That's probably what we'll do. > > > Yes, it is hard to predict what load this will create. The caching > levels around Wikipedia prevent re-computation of the page on most > page views, so maybe there would not actually be very many > repeated requests for the same query coming from tOne option could > be a dedicated caching layer just for such wiki uses. On the one > hand, the set of all embedded queries is known upfront (so, in > contrast to other uses, you already know which queries will be > asked). On the other hand, users may wish to do a forced refresh > his side. The main danger again seems to be bursts of activity (a > page getting a lot of edits in a short time, and each edit > invalidates the ParserCache and requires refetching query results). > On the positive side, this specific usage of WDQS can pass its own > caching parameters (which we can control), so if there is a caching > layer in place, one could react to issues on short notice by being > more conservative there than for other queries. > > The interesting thing about the wiki-embedding usage is that it > requires quick propagation of changes. Scenario: a user visits a > Wikipedia page with a map created from a query; the user finds an > outdated item on the map; she goes to Wikidata to fix it, and > refreshes (edits) the page to see the change. Now if she is too > quick, the change will not have made it into the query result yet > -- she could try in a minute or so. However, if we have a long > caching period, her first query will have populated the cache and > prevent the update from showing for the maximal amount of time (the > whole cache period). This seems like a case where long caching > would be rather bad for user experience. > > > I think it would be nice if having a graph with query on a page > does not too much adversely affect the time it takes to save a > page. (e.g. if running the query takes 20 seconds..., and instead > reuse cached query results) And not have such usage kill / > overwhelm the query service, is also important. > > If we incorporate entity usage or something like that, then maybe > that could be used to handle cache invalidation in cases something > used in a query changed. > > Cheers, Katie I believe that this could be solved most easily by not letting queries to be entered directly on wiki pages but have separate pages for them where one can examine the result and see the last run of the query and trigger a re-run. The page on the wiki embedding the query would then be independent from the query service but only use the query result stored somewhere in the wiki. This seems to be a very transparent way for the user to see the status of the query because it provides a separate page to "manage" the query. One could maybe also specify automatic run-intervals etc. Best regards Bene -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBCAAGBQJWxFeSAAoJECB5/QQloPPvFkoP/RIJ7uSn6wEQYVfzbtzpGkwX xRbjIkZOprybHwSFQwVwnR96uyjI+i9H7zhbWhS7Cy5Qp4DalmlTwaGy0etkFNHv OV/OtYEE0C7mBVtTYDW9G7XR483lxwb8FWgGk0Ia3ddp4n8xSsVSDLVOmLySyVP/ sQdMQyyAxzNmdE+fgMow1HWrT8jHpKZoiUNbsWBlMGF6sUHxCMM322urdM9oWXqc Nt+FJ8WSUqYAUfWLQ7XmHsg/8lIbPK9FC7j79uvSCCj6xeO0qJU5iJ8AqpIG6ErK HgeokPin8kjMJd9EmyxcPKICLCFDuyYvXRbC22ycPOh7gggiiNJoz+Om8NvE5Qs6 CvSuWf5BKxx3tXub5mNgOtuJYmO4wykRcONiPb+9DgEOaXOP+FvZhIRwOkTqry8k GWUkhvnCVia1hZqpUURifTjUa8eyyY9IhQCGDo/Kyw7Qn5OFaBPme8V7fB2iCj8d 5TGfPkpXfEQkhejKH9Rz5Ic60yD+FN/tHdq/e3u3L88up4onuYao/Lk4W5XRS/GX pi/w2UYo4djIsUUow41KjD+gPuDAEomOLu0A6Yzk1JnYwLT8A66xNKx2sgR7MEDu 7HpBGC6Lp8L8ZmbJ0E/3QM3S+3V336+eoTadBRavOWxRRnV7EtYSdmo9xAaS52+e rZ+Bcn3fgIl5feA1o377 =m+mG -----END PGP SIGNATURE----- _______________________________________________ Wikidata mailing list [email protected] https://lists.wikimedia.org/mailman/listinfo/wikidata
