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https://issues.apache.org/jira/browse/LUCENE-1606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12786557#action_12786557
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Robert Muir commented on LUCENE-1606:
-------------------------------------
here is an explanation of the cleanupPosition, and the cases it handles
Symbols:
A = \u0000 - \uD7FFF (lower BMP)
H = \uD800 - \uDBFFF (high/lead surrogates)
L = \uDC00 - \uDFFFF (low/trail surrogates)
Z = \uE000 - \uFFFF (upper BMP)
case 1:
// an illegal combination, where we have not yet enumerated into the supp. plane
// so we increment to H + \uDC00 (the lowest possible trail surrogate)
HA -> H \uDC00
HH -> H \uDC00
case 2:
// an illegal combination where we have already enumerated the supp. plane
// we must replace both H and L with \uE000 (the lowest possible "upper BMP")
HZ -> \uE000
case 3:
// an illegal combination where we have a trailing lead surrogate.
// we have not yet enumerated the supp plane, so append \uDC000 (lowest
possible trail surrogate)
// this is just like case 1, except in final position.
H$ -> H \uDC00
case 4/5:
// an unpaired low surrogate. this is invalid when not preceded by lead
surrogate
// (and if there was one, the above rules would have dealt with it already)
// in this case we have to bump to \uE0000 (the lowest possible "upper BMP")
unpaired L -> \uE000
> 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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