I could not find any documentation on the syntax automaton url filter accepts ? Any idea, I will update the wiki accordingly.
2011/6/4 MilleBii <[email protected]> > Regexes where not optimized against backtracking as I did not know. A > typical one looked like this : > > -.*\.domain\.*.* > > I guess something like this would be better and give less backtracking : > > http:\/\/www\.domain\..* > > As for the automaton no reason a priori since I really never looked at it. > Does it used TRIE like pattern matching ? Which would be very fast and > appropriate I guess. > I will have a go at it and see how it helps. Thx. > > > 2011/6/4 Julien Nioche <[email protected]> > >> As Kirby pointed out the automaton-based filter should be far more >> efficent >> + its syntax is more restricted than the regex one but not dissimilar. >> What do your filters look like? Any reason why you can't use the automaton >> instead? >> >> Julien >> >> On 4 June 2011 09:44, MilleBii <[email protected]> wrote: >> >> > 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- >> > >> >> >> >> -- >> * >> *Open Source Solutions for Text Engineering >> >> http://digitalpebble.blogspot.com/ >> http://www.digitalpebble.com >> > > > > -- > -MilleBii- > -- -MilleBii-
