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https://issues.apache.org/jira/browse/SOLR-2649?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13986408#comment-13986408
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Greg Pendlebury commented on SOLR-2649:
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I applied this patch to 4.7.2 Yesterday and tried it out on or dev servers. At
first I thought it was pretty bad and failed completely... but then I had a
good think and re-read everything on this ticket and this[1] article and
realised my understanding of the problem was flawed. Using just this patch in
isolation it converted all of the OR operators to AND operators with mm=100%.
Very confusing behaviour for our business area, but I realise now that it is
correct.
Perhaps the confusion stems from the way the q.op and mm parameters interact.
If the behaviour was to instead separate them more clearly then we could change
the config entirely. At the moment our mm is 100% because we effectively want
q.op=AND, but if q.op was instead applied 1) always, 2) first and 3)
independently from mm (ie. insert AND wherever an operator is missing) we could
set mm=1 and achieve what we want by respecting the OR parameters provided by
the user.
I've added this on top of the patch already here and deployed again to our dev
servers using 'q.op=AND & mm=1' and now everything appears to function as it
should. I'll upload the patch in a minute, and it includes several unit tests
with different mm and q.op values. From my perspective I think the two
parameters are interacting appropriately, but perhaps someone with more
convoluted mm settings could give it a try?
The change is simply in the constructor of the ExtendedSolrQueryParser class
where it was hardcoded to force the default operator to OR (presumably so that
mm would take care of things) I've made it look at the parameter provided with
the query (copied the code from the Simple QParser and adjusted to fit).
The unit test from the first patch that was marked TODO I have tweaked
slightly. I think not finding a result in that case is entirely appropriate if
the user can now tweak q.op. Opinions may vary of course.
[1] http://searchhub.org/2011/12/28/why-not-and-or-and-not/
> MM ignored in edismax queries with operators
> --------------------------------------------
>
> Key: SOLR-2649
> URL: https://issues.apache.org/jira/browse/SOLR-2649
> Project: Solr
> Issue Type: Bug
> Components: query parsers
> Reporter: Magnus Bergmark
> Priority: Minor
> Fix For: 4.9, 5.0
>
> Attachments: SOLR-2649.diff, SOLR-2649.patch
>
>
> Hypothetical scenario:
> 1. User searches for "stocks oil gold" with MM set to "50%"
> 2. User adds "-stockings" to the query: "stocks oil gold -stockings"
> 3. User gets no hits since MM was ignored and all terms where AND-ed
> together
> The behavior seems to be intentional, although the reason why is never
> explained:
> // For correct lucene queries, turn off mm processing if there
> // were explicit operators (except for AND).
> boolean doMinMatched = (numOR + numNOT + numPluses + numMinuses) == 0;
> (lines 232-234 taken from
> tags/lucene_solr_3_3/solr/src/java/org/apache/solr/search/ExtendedDismaxQParserPlugin.java)
> This makes edismax unsuitable as an replacement to dismax; mm is one of the
> primary features of dismax.
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