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https://issues.apache.org/jira/browse/LUCENE-1606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12780471#action_12780471
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Robert Muir commented on LUCENE-1606:
-------------------------------------
bq. That is a cool tradeoff to be able to make.
Mark, yes. I guess someone could implement the DFA-reversing if they wanted to,
to enable leading .* regex support with ReverseStringFilter.
you can still use this Wildcard impl with ReverseStringFilter just like the
core Wildcard impl, because its just so easy to reverse a wildcard string.
but you don't want to try to reverse a regular expression! that would be hairy.
easier to reverse a DFA.
but even without this, there are tons of workarounds, like the tradeoff i
mentioned earlier.
also, another one that might not be apparent is that its only the leading .*
that is a problem, depending on corpus of course.
[a-z].*abacadaba will avoid visiting terms that start with 1,2,3 or are in
chinese, etc, which might be a nice improvement.
of course if all your terms start with a-z, then its gonna be the same as
entering .*abacadaba, and be bad.
all depends on how selective the regular expression is wrt your terms.
> Automaton Query/Filter (scalable regex)
> ---------------------------------------
>
> Key: LUCENE-1606
> URL: https://issues.apache.org/jira/browse/LUCENE-1606
> 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
>
>
> 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 (http://www.brics.dk/automaton/) 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 do:
>
> 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 http://www.brics.dk/automaton/ and is BSD-licensed.
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