[jira] [Commented] (CASSANDRA-12078) [SASI] Move skip_stop_words filter BEFORE stemming

["DOAN DuyHai (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-12078?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15348240#comment-15348240 ] 

DOAN DuyHai commented on CASSANDRA-12078:
-----------------------------------------

I'll work on it this weekend and proposed a proprer patch with update Unit tests

> [SASI] Move skip_stop_words filter BEFORE stemming
> --------------------------------------------------
>
>                 Key: CASSANDRA-12078
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12078
>             Project: Cassandra
>          Issue Type: Bug
>          Components: sasi
>         Environment: Cassandra 3.7, Cassandra 3.8
>            Reporter: DOAN DuyHai
>            Assignee: DOAN DuyHai
>             Fix For: 3.8
>
>         Attachments: patch.txt
>
>
> Right now, if skip stop words and stemming are enabled, SASI will put stemming in the filter pipeline BEFORE skip_stop_words:
> {code:java}
>     private FilterPipelineTask getFilterPipeline()
>     {
>         FilterPipelineBuilder builder = new FilterPipelineBuilder(new BasicResultFilters.NoOperation());
>      ...
>         if (options.shouldStemTerms())
>             builder = builder.add("term_stemming", new StemmingFilters.DefaultStemmingFilter(options.getLocale()));
>         if (options.shouldIgnoreStopTerms())
>             builder = builder.add("skip_stop_words", new StopWordFilters.DefaultStopWordFilter(options.getLocale()));
>         return builder.build();
>     }
> {code}
> The problem is that stemming before removing stop words can yield wrong results.
> I have an example:
> {code:sql}
> SELECT * FROM music.albums WHERE country='France' AND title LIKE 'danse' ALLOW FILTERING;
> {code}
> Because of stemming *danse* ( *dance* in English) becomes *dans* (the final vowel is removed). Then skip stop words is applied. Unfortunately *dans* (*in* in English) is a stop word in French so it is removed completely.
> In the end the query is equivalent to {{SELECT * FROM music.albums WHERE country='France'}} and of course the results are wrong.
> Attached is a trivial patch to move the skip_stop_words filter BEFORE stemming filter
> /cc [~xedin] [~jrwest] [~beobal]



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