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https://issues.apache.org/jira/browse/LUCENE-1606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12780441#action_12780441
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Robert Muir commented on LUCENE-1606:
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bq. No problem in my mind - nothing the current WildcardQuery doesn't face. Any
reason we wouldn't want to replace the current WCQ that with this?
I don't think there is any issue. by implementing WildcardQuery with the DFA,
leading ? is no longer a problem,
i mean depending on your term dictionary if you do something stupid like
???????abacadaba it probably wont be that fast.
I spent a lot of time with the worst-case regex, wildcards to ensure
performance is at least as good as the other alternatives.
There is only one exception, the leading * wildcard is a bit slower with a DFA
than if you ran it with actual WildcardQuery (less than 5% in my tests)
Because of this, currently this patch rewrites this very special case to a
standard WildcardQuery.
bq. Now that sounds interesting - now sure I fully understand you though - are
you saying we can do a prefix match, but without having to index terms reversed
in the index? That would be very cool.
No, what I am saying is that you still have to index the terms in reversed
order for the leading */.* case, except then this reversing buys you faster
wildcard AND regex queries :)
> 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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