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Date: Tue, 10 Nov 2009 08:34:28 +0000 (UTC)
From: "Martijn van Groningen (JIRA)" <jira@apache.org>
To: solr-dev@lucene.apache.org
Subject: [jira] Commented: (SOLR-236) Field collapsing
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    [ https://issues.apache.org/jira/browse/SOLR-236?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12775350#action_12775350 ] 

Martijn van Groningen commented on SOLR-236:
--------------------------------------------

With the current patch if you try to collapse on a field that is tokenized or multivalued an exception is thrown indicating that you cannot do that and the search is cancelled. What I guess is that when the search results are retrieved from the shards on the master a NPE is thrown because the shard result is not there. This is a limitation in itself, but it boils down to the fact how the FieldCache handles such field types (or at least how I think the FieldCache handles it).

I think it is good idea to share your patch and from there we might be able to get the change in a proper manner. So others will also benefit from quasi-distributed field collapsing.

Anyhow to properly implement distributed field collapsing the distributed methods have to be overriden in the collapse component, so that is where I would start. We might then also include the collapse_count in the response.

> Field collapsing
> ----------------
>
>                 Key: SOLR-236
>                 URL: https://issues.apache.org/jira/browse/SOLR-236
>             Project: Solr
>          Issue Type: New Feature
>          Components: search
>    Affects Versions: 1.3
>            Reporter: Emmanuel Keller
>             Fix For: 1.5
>
>         Attachments: collapsing-patch-to-1.3.0-dieter.patch, collapsing-patch-to-1.3.0-ivan.patch, collapsing-patch-to-1.3.0-ivan_2.patch, collapsing-patch-to-1.3.0-ivan_3.patch, field-collapse-3.patch, field-collapse-4-with-solrj.patch, field-collapse-5.patch, field-collapse-5.patch, field-collapse-5.patch, field-collapse-5.patch, field-collapse-5.patch, field-collapse-5.patch, field-collapse-5.patch, field-collapse-5.patch, field-collapse-5.patch, field-collapse-solr-236-2.patch, field-collapse-solr-236.patch, field-collapsing-extended-592129.patch, field_collapsing_1.1.0.patch, field_collapsing_1.3.patch, field_collapsing_dsteigerwald.diff, field_collapsing_dsteigerwald.diff, field_collapsing_dsteigerwald.diff, SOLR-236-FieldCollapsing.patch, SOLR-236-FieldCollapsing.patch, SOLR-236-FieldCollapsing.patch, solr-236.patch, SOLR-236_collapsing.patch, SOLR-236_collapsing.patch
>
>
> This patch include a new feature called "Field collapsing".
> "Used in order to collapse a group of results with similar value for a given field to a single entry in the result set. Site collapsing is a special case of this, where all results for a given web site is collapsed into one or two entries in the result set, typically with an associated "more documents from this site" link. See also Duplicate detection."
> http://www.fastsearch.com/glossary.aspx?m=48&amid=299
> The implementation add 3 new query parameters (SolrParams):
> "collapse.field" to choose the field used to group results
> "collapse.type" normal (default value) or adjacent
> "collapse.max" to select how many continuous results are allowed before collapsing
> TODO (in progress):
> - More documentation (on source code)
> - Test cases
> Two patches:
> - "field_collapsing.patch" for current development version
> - "field_collapsing_1.1.0.patch" for Solr-1.1.0
> P.S.: Feedback and misspelling correction are welcome ;-)

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