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https://issues.apache.org/jira/browse/LUCENE-1606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12786542#action_12786542
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Robert Muir commented on LUCENE-1606:
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bq. Also going over the code, but thats going to take more time.
Btw, I will accept any criticism here. I am not happy with the complexity of
the enum in the trunk patch, personally.
But here are the three main issues that I think make it complex: (not to try to
place blame elsewhere)
* This trie<->DFA intersection is inherently something i would want to define
recursively, but this would be obviously bad.
* The DFA library uses UTF-16 whereas TermRef requires UTF-8. Changing
automaton to use 'int' would fix this, but then would destroy performance. The
reason brics is the fastest java regex library is that it tableizes the DFA
into a 64k UTF-16 char[]. See RunAutomaton for the impl. I think making this
require 1MB for the corner cases is bad.
* MultiTermQuerys that seek around are pretty complex in trunk. In my opinion
this enum is a lot easier to understand with the improvements Uwe is working on
for FilteredTermsEnum (see his branch patch, I think its easier there).
if you have ideas how we can simplify any of this in trunk for easier
readability (instead of just adding absurd amounts of comments as I did), I'd
be very interested.
> 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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