Just for the record the impact can be very very bad if you add too many regexes. I just finished a test and I got a factor 20 slower just for the generate step by adding 30 or so regexes in the filter. So beware.
2011/6/3 MilleBii <[email protected]> > Indeed I'm running a vertical search engine too however I want to improve > it as well on several front. > Scoring is one way but it does not prevent uninteresting content to > creep-in the crawld which eventually grows big/too big wasting ressources > for nothing. I > > Filtering is another way at the cost of a lot of regexes, hence this > question. > > Third I see crawldb pruning you want to ditch all urls that are below a > certain score. A question I asked a long time ago and the answer was write > your own mapred for that, a bit too far fetch for me insofar. > > What would be top for me is to be able to extract properties about > pages/urls in whatever phase scoring, indexing and be able to use those > properties during the generate phase as a kind of feedback loop. It is a > real pain to be forced to try to merge this information into a score > > > > 2011/6/2 Kirby Bohling <[email protected]> > >> I see from your e-mails that you are modifying the Scoring algorithm, >> the only other option I see is to write the scoring algorithm which >> detects that this is content you don't want to crawl, and this lowers >> the score. As I recall, links with the highest score are crawled >> first, so in the end that might be easier. Which sounds like it'd be >> writing a Vertical Search engine of some type (either that, or Spam >> detector with your personal/custom definition of Spam). >> >> I know several people on the this list or the dev list are writing >> vertical search engines, maybe they would have more thoughts or info. >> >> Kirby >> >> On Thu, Jun 2, 2011 at 3:47 PM, MilleBii <[email protected]> wrote: >> > Yes I remember reading that a few years ago. >> > But frankly I can't design by hand such finite automaton which will ever >> > changing by the way. >> > >> > Even adding regexes by hand, is most likely a daunting task for me. >> > >> > 2011/6/2 Kirby Bohling <[email protected]> >> > >> >> From what I remember of earlier advise, you really want to use the >> >> Automaton filter if at all possible, rather than series of straight >> >> regex. Using the Automaton should be linear with respect to the >> >> number of characters in the URL. Building the actual automaton could >> >> be fairly time consuming, but as you'll re-using it often, likely >> >> worth the cost. >> >> >> >> >> >> >> http://nutch.apache.org/apidocs-1.2/org/apache/nutch/urlfilter/automaton/package-summary.html >> >> >> >> A series of Java Regex's should also be linear with the number of >> >> characters in the URL assuming you avoid specific constructs (the >> >> things that cause back tracking, where it effectively tries to ensure >> >> that one group/subgroup is equal to a later group/subgroup is the >> >> primary culprit). Each Regex will add to the constant multiple in >> >> front of the number of characters. >> >> >> >> I've used the Automaton library, and if you can work within the >> >> limitations (it is a classic regex matcher with limited operators >> >> relative to say Perl 5 Compatible Regular Expressions). >> >> >> >> I don't have any practical experience with Nutch for a large scale >> >> crawl, but based upon my experience with using regular expressions and >> >> the Automaton Library, I know it is much faster. I recall Andrej >> >> talking about it being much faster. It might also be worth while for >> >> Nutch to look into Lucene's optimized versions of Automaton (they >> >> ported over several critical operations for use in Lucene and the >> >> Fuzzy matching when computing the Levenshtien distance). >> >> >> >> I can't seem to find the thread where I saw that advice given, but you >> >> can see the thread where they discuss adding the Automaton URL filter >> >> back in Nutch 0.8 and it seems to agree with my experience in using >> >> both. >> >> >> >> >> >> >> http://lucene.472066.n3.nabble.com/Much-faster-RegExp-lib-needed-in-nutch-td623308.html >> >> >> >> Kirby >> >> >> >> >> >> >> >> On Thu, Jun 2, 2011 at 2:42 PM, MilleBii <[email protected]> wrote: >> >> > What will be the impact of a growing big regex-urlfilter ? >> >> > >> >> > I ask this because there are more & more sites that I want to filter >> >> out, >> >> > it will limit the # of unecessary pages at a cost of lots of url >> >> > verification. >> >> > Side question since I already have pages from those sites in the >> crawldb, >> >> > will they be removed ever ? What would be the method to remove them ? >> >> > >> >> > -- >> >> > -MilleBii- >> >> > >> >> >> > >> > >> > >> > -- >> > -MilleBii- >> > >> > > > > -- > -MilleBii- > -- -MilleBii-
