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From Martijn v Groningen <>
Subject Re: Question about LUCENE-3097 - Post Group Faceting
Date Fri, 05 Aug 2011 08:22:51 GMT
Hi Josh,

For post grouping the documents don't need to reside in the same segment.
Lucene's grouping module has a collector (TermAllGroupHeadsCollector) that
collect the most relevant document for each group (GroupHead). This
collector can produce a int[] or a FixedBitSet that can be used during
faceting to produce
post group facets (patch in SOLR-2665 uses this). During faceting only the
the groupheads are known, because of this field values that are different in
less relevant than the most relevant document of a group aren't taken into
account. This is the same as in example described in the description of
Hope this helps!


On 4 August 2011 22:59, Joshua Harness <> wrote:

> Hello -
>      Please let me know if this question is more appropriate of the user
> list. I had assumed the developer list was more appropriate since the ticket
> is still open.  I was analyzing the comments on LUCENE-3097<>and
had a couple of questions.
>      A comment<>started
a small thread that mentioned that all documents in a given group
> would need to be contiguous and in the same segment. Also - a statement was
> made that ' The app would have to ensure this'. I was unclear the result of
> this conversation. It sounded like maybe this could have turned out to not
> be the case. What is the status of this? Does my application have to ensure
> all the documents in the group are in the same segment? How would one
> accomplish this?
>      Another comment<>mentioned
that 'we pick only the head long as the head doc is
> guaranteed to have the same value for field X, it safe to use that doc to
> represent the entire group for facet counting'.  Does this mean that there
> is a restriction placed on me that the head document must have field values
> that match the rest of the documents in the same group? Or is this simply an
> implementation detail that uses the head document when this condition is the
> case or chooses another strategy when this is not the case?
>      I am very interested in adopting this patch. However - I am attempting
> to understand any limitations/conditions so that I may use it correctly. Any
> advice would be greatly appreciated.
> Thanks!
> Josh Harness

Met vriendelijke groet,

Martijn van Groningen

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