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https://issues.apache.org/jira/browse/LUCENE-1370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12627343#action_12627343
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Karl Wettin commented on LUCENE-1370:
-------------------------------------
Do you say it is 50x faster with shingle queries that only contains bigram
compared to shingle queries that contains uni- and bigrams? Or is it 50x faster
using shingles compared to phrase queries? (I've myself seen performance gains
similar to the latter.)
> Patch to make ShingleFilter output a unigram if no ngrams can be generated
> --------------------------------------------------------------------------
>
> Key: LUCENE-1370
> URL: https://issues.apache.org/jira/browse/LUCENE-1370
> Project: Lucene - Java
> Issue Type: Improvement
> Components: contrib/analyzers
> Reporter: Chris Harris
> Attachments: ShingleFilter.patch
>
>
> Currently if ShingleFilter.outputUnigrams==false and the underlying token
> stream is only one token long, then ShingleFilter.next() won't return any
> tokens. This patch provides a new option, outputUnigramIfNoNgrams; if this
> option is set and the underlying stream is only one token long, then
> ShingleFilter will return that token, regardless of the setting of
> outputUnigrams.
> My use case here is speeding up phrase queries. The technique is as follows:
> First, doing index-time analysis using ShingleFilter (using
> outputUnigrams==true), thereby expanding things as follows:
> "please divide this sentence into shingles" ->
> "please", "please divide"
> "divide", "divide this"
> "this", "this sentence"
> "sentence", "sentence into"
> "into", "into shingles"
> "shingles"
> Second, do query-time analysis using ShingleFilter (using
> outputUnigrams==false and outputUnigramIfNoNgrams==true). If the user enters
> a phrase query, it will get tokenized in the following manner:
> "please divide this sentence into shingles" ->
> "please divide"
> "divide this"
> "this sentence"
> "sentence into"
> "into shingles"
> By doing phrase queries with bigrams like this, I can gain a very
> considerable speedup. Without the outputUnigramIfNoNgrams option, then a
> single word query would tokenize like this:
> "please" ->
> [no tokens]
> But thanks to outputUnigramIfNoNgrams, single words will now tokenize like
> this:
> "please" ->
> "please"
> ****
> The patch also adds a little to the pre-outputUnigramIfNoNgrams option tests.
> ****
> I'm not sure if the patch in this state is useful to anyone else, but I
> thought I should throw it up here and try to find out.
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