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From "Robert Muir (JIRA)" <>
Subject [jira] Commented: (LUCENE-1606) Automaton Query/Filter (scalable regex)
Date Fri, 20 Nov 2009 16:34:40 GMT


Robert Muir commented on LUCENE-1606:

bq. Yes - I think so - but how to handle the fact that you fall back to it? We might either
rename it or incorporate it into the new WildcardQuery?
We could just remove the .rewrite(). it is only that very special case, for leading *, where
the existing WildcardQuery logic is slightly faster (< 5%).
I was actually surprised the wildcardquery logic beats a DFA, i guess something to be said
for that hairy logic :)

bq. Shouldn't this one eventually make the old obsolete? I say we name it RegexQuery.
I do not know, all regex is not created equal. This one has different syntax and stuff from
the other impl's.
Any other ideas? Obviously the name RegexpQuery, with a p,  is available

bq. Yup - I think we should reformat and drop the author tags. We can mention that type of
info in the NOTICE file.
ok, this is easy, i already have NOTICE in the patch. i was sure all files from brics have
their license header also.

bq. I think so - perhaps util.brics? No need for dk I don't think.

> Automaton Query/Filter (scalable regex)
> ---------------------------------------
>                 Key: LUCENE-1606
>                 URL:
>             Project: Lucene - Java
>          Issue Type: New Feature
>          Components: contrib/*
>            Reporter: Robert Muir
>            Assignee: Robert Muir
>            Priority: Minor
>             Fix For: 3.1
>         Attachments: automaton.patch, automatonMultiQuery.patch, automatonmultiqueryfuzzy.patch,
automatonMultiQuerySmart.patch, automatonWithWildCard.patch, automatonWithWildCard2.patch,
LUCENE-1606.patch, LUCENE-1606.patch, LUCENE-1606_nodep.patch
> Attached is a patch for an AutomatonQuery/Filter (name can change if its not suitable).
> Whereas the out-of-box contrib RegexQuery is nice, I have some very large indexes (100M+
unique tokens) where queries are quite slow, 2 minutes, etc. Additionally all of the existing
RegexQuery implementations in Lucene are really slow if there is no constant prefix. This
implementation does not depend upon constant prefix, and runs the same query in 640ms.
> Some use cases I envision:
>  1. lexicography/etc on large text corpora
>  2. looking for things such as urls where the prefix is not constant (http:// or ftp://)
> The Filter uses the BRICS package ( to convert regular
expressions into a DFA. Then, the filter "enumerates" terms in a special way, by using the
underlying state machine. Here is my short description from the comments:
>      The algorithm here is pretty basic. Enumerate terms but instead of a binary accept/reject
>      1. Look at the portion that is OK (did not enter a reject state in the DFA)
>      2. Generate the next possible String and seek to that.
> the Query simply wraps the filter with ConstantScoreQuery.
> I did not include the automaton.jar inside the patch but it can be downloaded from
and is BSD-licensed.

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