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https://issues.apache.org/jira/browse/LUCENE-1606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12786566#action_12786566
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Robert Muir commented on LUCENE-1606:
-------------------------------------
btw one thing we could do is put this nextValidUTF16String in UnicodeUtil and
also use it in SegmentReader.LegacyTermEnum to replace the "hack", just in case
someone else wrote an enum like mine.
this would provide better backwards compatibility, as they would receive the
'next Term' in IndexReader.terms() just as they did before, even if the term is
completely jacked...
below is the existing hack:
{code}
// this is a hack only for backwards compatibility.
// previously you could supply a term ending with a lead surrogate,
// and it would return the next Term.
// if someone does this, tack on the lowest possible trail surrogate.
// this emulates the old behavior, and forms "valid UTF-8" unicode.
if (text.length() > 0
&& Character.isHighSurrogate(text.charAt(text.length() - 1)))
tr = new TermRef(t.text() + "\uDC00");
else
tr = new TermRef(t.text());
{code}
instead it could read something like tr = new
TermRef(UnicodeUtil.nextValidUTF16String(t.text()));
> 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.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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