On Tue, Apr 10, 2012 at 11:55 AM, Christian Stocker <[email protected]> wrote: > > > On 10.04.12 11:51, Ard Schrijvers wrote: >> On Tue, Apr 10, 2012 at 11:42 AM, Christian Stocker >> <[email protected]> wrote: >>> >>> >>> On 10.04.12 11:32, Ard Schrijvers wrote: >>>> On Tue, Apr 10, 2012 at 11:21 AM, Lukas Kahwe Smith <[email protected]> >>>> wrote: >>>>> Hi, >>>>> >>>>> Currently I see some big issues with queries that return large result >>>>> sets. A lot of work is not done inside Lucene, which will probably not be >>>>> fixed soon (or maybe never inside 2.x). However I think its important to >>>>> do some intermediate improvements. >>>>> >>>>> Here are some suggestions I have. I hope we can brainstorm together on >>>>> some ideas that are feasible to get implemented in a shorter time period >>>>> than waiting for Oak: >>>>> >>>>> 1) there should be a way to get a count >>>>> >>>>> This way if I need to do a query that needs to be ordered, I can first >>>>> check if the count is too high to determine if I should even bother >>>>> running the search. Aka in most cases a search leading to 100+ results >>>>> means that who ever did the search needs to further narrow it down. >>>> >>>> The cpu is not spend in ordering the results: That is done quite fast >>>> in Lucene, unless you have millions of hits >>> >>> I read the code and also read this >>> https://issues.apache.org/jira/browse/JCR-2959 and it looks to me that >>> jackrabbit always sorts the result set by itself and not in lucene (or >>> maybe additionally). This makes it slow even if you have a limit set, >>> because it first sorts all nodes (fetching it from the PM if necessary), >>> then does the limit. Maybe I have missed something but real life tests >>> showed exactly this behaviour. >> >> Ah, I don't know about that part: We always sticked to xpath queries : >> Sorting is done in Lucene (more precisely, in some Lucene exensions in >> jr, but are equally fast) for at least xpath, I am quite sure > > Is the search part done differently in SQL2 and XPath? Can't remember ;)
I think in some areas, but, it should pretty much result in the same Lucene queries. I've never looked into SQL2 : But, because you pointed at [1] and it there explicitly mentioned SQL2, and since we don't have this problem, I thought it would be SQL2 only [1] https://issues.apache.org/jira/browse/JCR-2959 > >>>> The problem with getting a correct count is authorization : This total >>>> search index count should is fast (if you try to avoid some known slow >>>> searches). However, authorizing for example 100k+ nodes if they are >>>> not in the jackrabbit caches is very expensive. >>>> >>>> Either way: You get a correct count if you make sure that you include >>>> in your (xpath) search at least an order by clause. Then, to avoid >>>> 100k + hits, make sure you also set a limit. For example a limit of >>>> 501 : You can then show 50 pages of 10 hits, and if the count is 501 >>>> you state that there are at least 500+ hits >>> >>> That's what we do now, but it doesn't help (as said above) if we have >>> thousends of results which have to be ordered first. >> >> And the second sort is also slow? The first sort is also slow with >> Lucene, as Lucene needs to load all terms to sort on from FS in >> memory. However, consecutive searches are fast. We don't have problems >> for resultsets sorting for a million hits > > It definitively loaded all nodes from the PM before sorting it. The > lucene part itself was fast enough, that wasn't the issue. > >> >>> >>>> >>>> We also wanted to get around this, thus in our api hooked in a >>>> 'getTotalSize()' which returns the Lucene unauthorized count >>> >>> That would help us a lot, since we currently don't use the ACLs of >>> Jackrabbit, so the lucene count would be pretty correct for our use case. >> >> Yes, however, you would have to hook into jr itself to get this done > > Yep, saw that, that's somewhere deep in the code. That's why I didn't > try to adress that yet > > chregu > >> >> Regards Ard >> >>> >>> chregu >>> >>>> >>>>> >>>>> I guess the most sensible thing would be to simply offer a way to do >>>>> SELECT COUNT(*) FROM .. >>>>> >>>>> 2) a way to automatically stop long running queries >>>> >>>> It is not just about 'long' . Some queries easily blow up, and bring >>>> you app to an OOM before they can be stopped. For example jcr:like is >>>> such a thing. Or range queries on many unique values >>> >>> >>>> >>>> Regards Ard >>>> >>>>> >>>>> It would be great if one could define a timeout for queries. If a query >>>>> takes longer than X, it should just fail. This should be a global >>>>> setting, but ideally it should be possible to override this on a per >>>>> query basis. >>>>> >>>>> 3) .. ? >>>>> >>>>> regards, >>>>> Lukas Kahwe Smith >>>>> [email protected] >>>>> >>>>> >>>>> >>>> >>>> >>>> >>> >>> -- >>> Liip AG // Feldstrasse 133 // CH-8004 Zurich >>> Tel +41 43 500 39 81 // Mobile +41 76 561 88 60 >>> www.liip.ch // blog.liip.ch // GnuPG 0x0748D5FE >>> >> >> >> > > -- > Liip AG // Feldstrasse 133 // CH-8004 Zurich > Tel +41 43 500 39 81 // Mobile +41 76 561 88 60 > www.liip.ch // blog.liip.ch // GnuPG 0x0748D5FE > -- Amsterdam - Oosteinde 11, 1017 WT Amsterdam Boston - 1 Broadway, Cambridge, MA 02142 US +1 877 414 4776 (toll free) Europe +31(0)20 522 4466 www.onehippo.com
