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https://issues.apache.org/jira/browse/LUCENE-1606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12781220#action_12781220
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Robert Muir commented on LUCENE-1606:
-------------------------------------

bq. We can discuss this under the new [separately] "optimization" issue for 
MTQs?

is there a jira issue for this??

bq. Also, remember that the current API is doing not only new String() but also 
new Term() when it enums the terms, so having to do new String() for MTQs on 
flex API is OK for starters.

oh yeah, its clear the flex api is already better, from benchmarks.
I am just trying to think of ways to make it both faster, at the same time easy 
too.

> 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: Search
>            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, 
> BenchWildcard.java, LUCENE-1606-flex.patch, LUCENE-1606.patch, 
> LUCENE-1606.patch, LUCENE-1606.patch, LUCENE-1606.patch, LUCENE-1606.patch, 
> LUCENE-1606.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 (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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