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From "Robert Muir (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1606) Automaton Query/Filter (scalable regex)
Date Sun, 22 Nov 2009 21:47:39 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12781227#action_12781227
] 

Robert Muir commented on LUCENE-1606:
-------------------------------------

bq. Actually... wouldn't we need to convert to int[] (for Unicode 4) not char[], to be most
convenient for "higher up" APIs like automaton? If we did char[] you'd still have to handle
surrogates process (and then it's not unlike doing byte[]).

I wanted to make another comment here, I agree that this somewhat like byte[].
But there are some major differences:
# the java API provides mechanisms in Character, etc for processing text this way.
# lots of stuff is unaffected. for example .startsWith() is not broken for supp characters.
 it does not have to use codepoint anywhere, can just compare chars, which are surrogates,
but this is ok.
 so lots of char[]-based processing is already compatible, and completely unaware of this
issue. this is not true for byte[]
# it will perform the best overall, its only needed in very few places and we can be very
careful where we add these checks, so we don't slow anything down or increase RAM usage, etc.

> 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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