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https://issues.apache.org/jira/browse/LUCENE-2458?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Robert Muir updated LUCENE-2458:
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Attachment: LUCENE-2458.patch
Attached is a patch that addresses most of the issue:
NOTE: I do not tackle the 'split on whitespace' issue as this is a larger
change and would require changes to the actual grammar itself. We can open a
separate JIRA issue for this. This issue is about not generating phrase queries
based on how many terms come out of the hardcoded whitespace-tokenizer in
QueryParser.
* The bug is preserved based on both Version and subclassing, so previous
subclasses overriding getFieldQuery work just fine as before.
* All lucene/solr tests pass, the backwards/ still uses LUCENE_CURRENT so i had
to add a TEST_VERSION_CURRENT there, so that it runs the tests as LUCENE_30
(this is a problem in general).
* This fixes a host of issues for CJK, not only do we let normal queries work,
but phrase/sloppy phrase work correctly too if you use the double quotes.
(because if you use PositionFilter hack you disable these!)
* Normal CJK queries also get coord(), which if you use the PositionFilter hack
is disabled too, because it treates the entire query as synonyms. CJK users
should get coord() too, like english users, thanks to Ivan for testing this
(additional 12% relevance boost on their test collection).
* Normal CJK queries are formed by the queryparser default operator, same as
english queries.
* English synonym queries (1 term followed by multiple positions) still get
coord() disabled as they should.
* I only migrated one subclass to the new API, the "Extendable Query Parser",
and only because its TestExtendable actually extends TestQueryParser from core
(so it had to be done).
TODO:
* The coord-disabled-BQ code for english synonyms need to be generalized in
case CJK users use synonyms, single terms followed by posinc=0 terms should
form coord-disabled-BQ's just like they do for english.
* Add some nice explicit tests for CJK queries, phrase queries, sloppy phrase
queries, CJK queries with synonyms, etc.
* Cutover remaining queryparsers
> queryparser shouldn't generate phrasequeries based on term count
> ----------------------------------------------------------------
>
> Key: LUCENE-2458
> URL: https://issues.apache.org/jira/browse/LUCENE-2458
> Project: Lucene - Java
> Issue Type: Bug
> Components: QueryParser
> Reporter: Robert Muir
> Priority: Critical
> Attachments: LUCENE-2458.patch
>
>
> The current method in the queryparser to generate phrasequeries is wrong:
> The Query Syntax documentation
> (http://lucene.apache.org/java/3_0_1/queryparsersyntax.html) states:
> {noformat}
> A Phrase is a group of words surrounded by double quotes such as "hello
> dolly".
> {noformat}
> But as we know, this isn't actually true.
> Instead the terms are first divided on whitespace, then the analyzer term
> count is used as some sort of "heuristic" to determine if its a phrase query
> or not.
> This assumption is a disaster for languages that don't use whitespace
> separation: CJK, compounding European languages like German, Finnish, etc. It
> also
> makes it difficult for people to use n-gram analysis techniques. In these
> cases you get bad relevance (MAP improves nearly *10x* if you use a
> PositionFilter at query-time to "turn this off" for chinese).
> For even english, this undocumented behavior is bad. Perhaps in some cases
> its being abused as some heuristic to "second guess" the tokenizer and piece
> back things it shouldn't have split, but for large collections, doing things
> like generating phrasequeries because StandardTokenizer split a compound on a
> dash can cause serious performance problems. Instead people should analyze
> their text with the appropriate methods, and QueryParser should only generate
> phrase queries when the syntax asks for one.
> The PositionFilter in contrib can be seen as a workaround, but its pretty
> obscure and people are not familiar with it. The result is we have bad
> out-of-box behavior for many languages, and bad performance for others on
> some inputs.
> I propose instead that we change the grammar to actually look for double
> quotes to determine when to generate a phrase query, consistent with the
> documentation.
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