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From "Earwin Burrfoot (JIRA)" <>
Subject [jira] Commented: (SOLR-236) Field collapsing
Date Sun, 07 Jun 2009 23:42:07 GMT


Earwin Burrfoot commented on SOLR-236:

I have implemented collapsing on a high-volume project of mine in much less flexible, but
more practical manner.

Part I. You have to guarantee that all documents having the same value of collapse-field are
dropped into Lucene index as a sequential batch. That guarantees they get sequential docIds,
and with some more work - that they all end up in the same segment.
Part II. When doing collection you always get docIds in sequential order, and thus, thanks
to Part I you get the docs-to-be-collapsed already grouped by collapse-field, even before
you drop the docs into PriorityQueue to sort them.

You can only collapse on a single predetermined at index creation time field.
If one document changes, you have to reindex all docs that have the same collapse-field value,
so it's best if you have either low update/add rates, or few documents sharing the same collapse-field

The CPU and memory costs for collapsing compared to usual search are very close to zero and
do not depend on index size/total docs found.
The same idea works with new Lucene per-segment collection and in distributed mode (sharded
Within collapsed group you can sort hits however you want, and select one that will represent
the group for usual sort/paging.
The implementation is not brain-dead simple, but nears it.

> Field collapsing
> ----------------
>                 Key: SOLR-236
>                 URL:
>             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-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."
> 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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