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https://issues.apache.org/jira/browse/LUCENE-1606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12786555#action_12786555
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Robert Muir commented on LUCENE-1606:
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yes, Mark you have it right. This is not an issue for trunk, only flex, but I
fixed it ahead of time to prevent problems.
so i have a chinese example here:
https://issues.apache.org/jira/browse/LUCENE-1606?focusedCommentId=12785034&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#action_12785034
but at the same time, this kind of thing can happen with a simple wildcard *,
or ?
Because a wildcard ? will be converted into a UTF-16 DFA transition of
\u0000-\uFFFF, when enumerating this transition (depending on your term
dictionary), we cannot create a nextString for example that ends with say,
\uD800, else it will get replaced with \uFFFD, and we will miss terms.
The enumeration in nextString is greedy, so we can't just look for these in
final position either. For example, if you have a regexp of [lm]ar[kl], this
enum first tries to seek to lark (it will continue to walk transitions until an
accept state or a loop).
> 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-flex.patch,
> LUCENE-1606-flex.patch, LUCENE-1606-flex.patch, LUCENE-1606-flex.patch,
> 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.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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