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From Diego Ceccarelli <diego.ceccare...@gmail.com>
Subject Re: Rerank queries and grouping
Date Thu, 16 Jul 2015 08:22:55 GMT
Hi Joel,

Thanks for your reply,
Yes, I considered the Collapse and Expand [1] , the problem is that I'll
deploy it
on a multishard instance and I want to retrieve the top N groups.
I thing that collapse and expand could have two downsides:

i) it won't guarantee the retrieval of N groups, I could mitigate
retrieving a larger number of documents,
but I would prefer to avoid.
ii) It won't guarantee to have the best document per group: a shard A could
have high scoring documents in a group G1, and then have a top scoring
document D for the group G2, but since each shard returns only its top
documents, potentially I could  lose D as head of the group G2, if another
shard returns documents in G2 with a lower score.

Cheers,
Diego

[1]
https://cwiki.apache.org/confluence/display/solr/Collapse+and+Expand+Results

On Thu, Jul 16, 2015 at 2:01 AM, Joel Bernstein <joelsolr@gmail.com> wrote:

> As you've seen RankQueries won't currently have any effect on Grouping
> queries.
>
> A RankQuery can be combined with Collapse and Expand though. You may want
> to review Collapse and Expand and see if it meets your use case.
>
> Joel Bernstein
> http://joelsolr.blogspot.com/
>
> On Wed, Jul 15, 2015 at 2:36 PM, Diego Ceccarelli <
> diego.ceccarelli@gmail.com> wrote:
>
> > Hi Everyone,
> >
> > I need to use a RankQuery within a grouping [1].
> > I did some experiments with RerankQuery [2]  and solr 4.10.2 and it seems
> > that
> > if you group on a field, the reranking query is completely ignored
> > (on the cloud, and on a single instance).
> > I would expect to see the results in each group reranked using the
> > RerankQuery.
> >
> > I had a look at the grouping code and documentation and,
> > if I correctly understood, the grouping works in two steps:
> >
> > 1) first the top groups are retrieved
> > 2) top documents for each group in the top groups are retrieved.
> >
> > I thought that the collector generated by a RankQuery could be injected
> > in 2), i.e., for each group set a rerank collector... but I'm not sure if
> > this solution
> > is feasable since the collectors are set in Lucene
> > (AbstractSecondPassGroupingCollector)
> > and a RankQuery is defined in Solr...
> >
> > Any suggestion?
> >
> > Thanks,
> > Diego
> >
> > [1] https://cwiki.apache.org/confluence/display/solr/Result+Grouping
> > [2] https://cwiki.apache.org/confluence/display/solr/Query+Re-Ranking
> >
>

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