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From "Mark Miller (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1606) Automaton Query/Filter (scalable regex)
Date Sat, 18 Apr 2009 17:31:14 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12700511#action_12700511
] 

Mark Miller commented on LUCENE-1606:
-------------------------------------

When refactoring multitermquery I tried just computing the bit set iterator on the fly. It
did not appear to work out, but I wonder if there are cases where it would be a better option.

bq.For example, if the language of the automaton is infinite (for example, built from a regular
expression/wildcard with a * operator), it seems best to set constant score rewrite=true.

Okay, that starts to make more sense then. I think the reports that it was faster on some
large indexes was based on wildcard queries I think (hard to remember 100%).



> 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
>            Priority: Minor
>             Fix For: 2.9
>
>         Attachments: automaton.patch, automatonMultiQuery.patch, automatonWithWildCard.patch,
automatonWithWildCard2.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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