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https://issues.apache.org/jira/browse/LUCENE-2458?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12867143#action_12867143
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Yonik Seeley commented on LUCENE-2458:
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bq. Instead the queryparser should only form phrasequeries when you use double
quotes, just like the documentation says.
We're conflating high level user syntax and the underlying implementation.
'text:Ready' says "search for the word 'ready' in the field 'text'"... the fact
that an underlying term query of 'text:readi' (after lowercasing, stemming,
etc) is not incorrect, it's simply the closest match to what the user is asking
for given the details of analysis. Likewise, a user query of 'text:ak-47' may
end up as a phrase query of "ak 47" because that's the closest representation
in the index (the user doesn't necessarily know that the analysis of the field
splits on dashes).
Likewise, a user query of text:"foo bar" is a high level way of saying "search
for the word foo immediately followed by the word bar". It is *not* saying
"make a Lucene phrase query object with 2 terms". Synonyms, common grams, or
other analysis methods may in fact turn this into a single term query.
> 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
>
> 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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