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From "Stefan Trcek (JIRA)" <>
Subject [jira] [Commented] (LUCENE-3079) Facetiing module
Date Wed, 22 Jun 2011 17:34:47 GMT


Stefan Trcek commented on LUCENE-3079:

This patch was generated by git and tested to apply with
patch -p0 -i LUCENE-3079.patch --dry-run
Be patient if anything went wrong.

Review starting points may be
- FacetSearcherTest.testSimpleFacetWithIndexSearcher() or
- FacetSearcher.facetCollectSearch() may be  dismissed in favor of Guava.
If you are willing to keep it I'll strip it down to the required parts.


The implementation relies on field cache only, no index scheme, no 
cached filters etc. It supports
- single valued facets (
- multi valued facets (
- facet filters (see
- evaluation of facet values that would dismiss due to other facet 
filters (Yonik says Solr calls this "multi-select faceting").
(realized by FacetSearcher.fillFacetsForGuiMode())

Let me explain the last point: For the user a facet query
  (color==green) AND (shape==circle OR shape==square)
may look like

Facet color
[ ] (3) red
[x] (5) green
[ ] (7) blue

Facet shape
[x] (9) circle
[ ] (4) line
[x] (2) square

The red/blue/line facet values will display even though the 
corresponding documents are not in the result set. Also there is 
support for filtered facet values with zero results, so users 
understand why they do not get results.

> Facetiing module
> ----------------
>                 Key: LUCENE-3079
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>            Reporter: Michael McCandless
>         Attachments: LUCENE-3079.patch
> Faceting is a hugely important feature, available in Solr today but
> not [easily] usable by Lucene-only apps.
> We should fix this, by creating a shared faceting module.
> Ideally, we factor out Solr's faceting impl, and maybe poach/merge
> from other impls (eg Bobo browse).
> Hoss describes some important challenges we'll face in doing this
> (, copied here:
> {noformat}
> To look at "faceting" as a concrete example, there are big the reasons 
> faceting works so well in Solr: Solr has total control over the 
> index, knows exactly when the index has changed to rebuild caches, has a 
> strict schema so it can make sense of field types and 
> pick faceting algos accordingly, has multi-phase distributed search 
> approach to get exact counts efficiently across multiple shards, etc...
> (and there are still a lot of additional enhancements and improvements 
> that can be made to take even more advantage of knowledge solr has because 
> it "owns" the index that we no one has had time to tackle)
> {noformat}
> This is a great list of the things we face in refactoring.  It's also
> important because, if Solr needed to be so deeply intertwined with
> caching, schema, etc., other apps that want to facet will have the
> same "needs" and so we really have to address them in creating the
> shared module.
> I think we should get a basic faceting module started, but should not
> cut Solr over at first.  We should iterate on the module, fold in
> improvements, etc., and then, once we can fully verify that cutting
> over doesn't hurt Solr (ie lose functionality or performance) we can
> later cutover.

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