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From Erick Erickson <>
Subject Re: RegexQuery performance
Date Sun, 11 Dec 2011 02:25:42 GMT
Hmmm, I don't know all that much about the universe
you're searching (I'm *really* sorry about that, but I
couldn't resist) but I wonder if you can't turn the problem
on its head and do your regex stuff at index time instead.

My off-the-top-of-my-head notion is you implement a
Filter whose job is to emit some "special" tokens when
you find strings like this that allow you to search without
regexes. For instance, in the example you give, you could
index something like...oh... I don't know, ###VER### as
well as the "normal" text of "IRAS-A-FPA-3-RDR-IMPS-V6.0".
Now, when searching for docs with the pattern you used
as an example, you look for ###VER### instead. I guess
it all depends on how many regexes you need to allow.
This wouldn't work at all if you allow users to put in arbitrary
regexes, but if you have a small enough number of patterns
you'll allow, something like this could work.

The Filter I'm thinking of might behave something like a
SynonymFilter and emit multiple tokens at the same position.
You'd have to take some care that the *query* part of the
analyzer chain didn't undo whatever special symbols you used,
but that's all do-able.

I guess the idea here is that if you can map out all the kinds
of regex patterns you want to apply at query time and apply
them at index time instead it might work. Then you have to
work out how to allow the users to pick the special patterns,
but that's a UI problem...

>From a fortune cookie:
"A programmer had a problem that he tried to solve with
regular expressions. Now he has two problems" <G>


On Sat, Dec 10, 2011 at 9:20 AM, Jay Luker <> wrote:
> Hi Erick,
> On Fri, Dec 9, 2011 at 12:37 PM, Erick Erickson <> wrote:
>> Could you show us some examples of the kinds of things
>> you're using regex for? I.e. the raw text and the regex you
>> use to match the example?
> Sure!
> An example identifier would be "IRAS-A-FPA-3-RDR-IMPS-V6.0", which
> identifies a particular Planetary Data System data set. Another
> example is "ULY-J-GWE-8-NULL-RESULTS-V1.0". These kind of strings
> frequently appear in the references section of the articles, so the
> context looks something like,
> " ... rvey. IRAS-A-FPA-3-RDR-IMPS-V6.0, NASA Planetary Data System
> Tholen, D. J. 1989, in Asteroids II, ed ... "
> The simple & straightforward regex I've been using is
> /[A-Z0-9:\-]+V\d+\.\d+/. There may be a smarter regex approach but I
> haven't put my mind to it because I assumed the primary performance
> issue was elsewhere.
>> The reason I ask is that perhaps there are other approaches,
>> especially thinking about some clever analyzing at index time.
>> For instance, perhaps NGrams are an option. Perhaps
>> just making WordDelimiterFilterFactory do its tricks. Perhaps.....
> WordDelimiter does help in the sense that if you search for a specific
> identifier you will usually find fairly accurate results, even for
> cases where the hyphens resulted in the term being broken up. But I'm
> not sure how WordDelimiter can help if I want to search for a pattern.
> I tried a few tweaks to the index, like putting a minimum character
> count for terms, making sure WordDelimeter's preserveOriginal is
> turned on, indexing without lowercasing so that I don't have to use
> Pattern.CASE_INSENSITIVE. Performance was not improved significantly.
> The new RegexpQuery mentioned by R. Muir looks promising, but I
> haven't built an instance of trunk yet to try it out. Any ohter
> suggestions appreciated.
> Thanks!
> --jay
>> In other words, this could be an "XY problem"....
>> Best
>> Erick
>> On Thu, Dec 8, 2011 at 11:14 AM, Robert Muir <> wrote:
>>> On Thu, Dec 8, 2011 at 11:01 AM, Jay Luker <> wrote:
>>>> Hi,
>>>> I am trying to provide a means to search our corpus of nearly 2
>>>> million fulltext astronomy and physics articles using regular
>>>> expressions. A small percentage of our users need to be able to
>>>> locate, for example, certain types of identifiers that are present
>>>> within the fulltext (grant numbers, dataset identifers, etc).
>>>> My straightforward attempts to do this using RegexQuery have been
>>>> successful only in the sense that I get the results I'm looking for.
>>>> The performance, however, is pretty terrible, with most queries taking
>>>> five minutes or longer. Is this the performance I should expect
>>>> considering the size of my index and the massive number of terms? Are
>>>> there any alternative approaches I could try?
>>>> Things I've already tried:
>>>>  * reducing the sheer number of terms by adding a LengthFilter,
>>>> min=6, to my index analysis chain
>>>>  * swapping in the JakartaRegexpCapabilities
>>>> Things I intend to try if no one has any better suggestions:
>>>>  * chunk up the index and search concurrently, either by sharding or
>>>> using a RangeQuery based on document id
>>>> Any suggestions appreciated.
>>> This RegexQuery is not really scalable in my opinion, its always
>>> linear to the number of terms except in super-rare circumstances where
>>> it can compute a "common prefix" (and slow to boot).
>>> You can try svn trunk's RegexpQuery <-- don't forget the "p", instead
>>> from lucene core (it works from queryparser: /[ab]foo/, myfield:/bar/
>>> etc)
>>> The performance is faster, but keep in mind its only as good as the
>>> regular expressions, if the regular expressions are like /.*foo.*/,
>>> then
>>> its just as slow as wildcard of *foo*.
>>> --

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