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https://issues.apache.org/jira/browse/SOLR-4465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13693926#comment-13693926
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Joel Bernstein commented on SOLR-4465:
--------------------------------------
Greg,
On task number two I'm wondering if we could use the standard post filter
approach to inject new collectors. Then all we would need is a search component
that handles the merge from the shards. This approach could be done with
plugins so we wouldn't have to alter the core. The main work then would be a
search component that would allow for pluggable merging algorithms. This could
be useful in many contexts. We'd need to see how this component would fit in
the distributed flow.
Joel
> Configurable Collectors
> -----------------------
>
> Key: SOLR-4465
> URL: https://issues.apache.org/jira/browse/SOLR-4465
> Project: Solr
> Issue Type: New Feature
> Components: search
> Affects Versions: 4.1
> Reporter: Joel Bernstein
> Fix For: 4.4
>
> Attachments: SOLR-4465.patch, SOLR-4465.patch, SOLR-4465.patch,
> SOLR-4465.patch, SOLR-4465.patch, SOLR-4465.patch, SOLR-4465.patch,
> SOLR-4465.patch, SOLR-4465.patch, SOLR-4465.patch, SOLR-4465.patch,
> SOLR-4465.patch, SOLR-4465.patch, SOLR-4465.patch, SOLR-4465.patch,
> SOLR-4465.patch, SOLR-4465.patch
>
>
> This ticket provides a patch to add pluggable collectors to Solr. This patch
> was generated and tested with Solr 4.1.
> This is how the patch functions:
> Collectors are plugged into Solr in the solconfig.xml using the new
> collectorFactory element. For example:
> <collectorFactory name="default" class="solr.CollectorFactory"/>
> <collectorFactory name="sum" class="solr.SumCollectorFactory"/>
> The elements above define two collector factories. The first one is the
> "default" collectorFactory. The class attribute points to
> org.apache.solr.handler.component.CollectorFactory, which implements logic
> that returns the default TopScoreDocCollector and TopFieldCollector.
> To create your own collectorFactory you must subclass the default
> CollectorFactory and at a minimum override the getCollector method to return
> your new collector.
> The parameter "cl" turns on pluggable collectors:
> cl=true
> If cl is not in the parameters, Solr will automatically use the default
> collectorFactory.
> *Pluggable Doclist Sorting With the Docs Collector*
> You can specify two types of pluggable collectors. The first type is the docs
> collector. For example:
> cl.docs=<name>
> The above param points to a named collectorFactory in the solrconfig.xml to
> construct the collector. The docs collectorFactorys must return a collector
> that extends the TopDocsCollector base class. Docs collectors are responsible
> for collecting the doclist.
> You can specify only one docs collector per query.
> You can pass parameters to the docs collector using local params syntax. For
> example:
> cl.docs=\{! sort=mycustomesort\}mycollector
> If cl=true and a docs collector is not specified, Solr will use the default
> collectorFactory to create the docs collector.
> *Pluggable Custom Analytics With Delegating Collectors*
> You can also specify any number of custom analytic collectors with the
> "cl.analytic" parameter. Analytic collectors are designed to collect
> something else besides the doclist. Typically this would be some type of
> custom analytic. For example:
> cl.analytic=sum
> The parameter above specifies a analytic collector named sum. Like the docs
> collectors, "sum" points to a named collectorFactory in the solrconfig.xml.
> You can specificy any number of analytic collectors by adding additional
> cl.analytic parameters.
> Analytic collector factories must return Collector instances that extend
> DelegatingCollector.
> A sample analytic collector is provided in the patch through the
> org.apache.solr.handler.component.SumCollectorFactory.
> This collectorFactory provides a very simple DelegatingCollector that groups
> by a field and sums a column of floats. The sum collector is not designed to
> be a fully functional sum function but to be a proof of concept for pluggable
> analytics through delegating collectors.
> You can send parameters to analytic collectors with solr local param syntax.
> For example:
> cl.analytic=\{! id=1 groupby=field1 column=field2\}sum
> The "id" parameter is mandatory for analytic collectors and is used to
> identify the output from the collector. In this example the "groupby" and
> "column" params tell the sum collector which field to group by and sum.
> Analytic collectors are passed a reference to the ResponseBuilder and can
> place maps with analytic output directory into the SolrQueryResponse with the
> add() method.
> Maps that are placed in the SolrQueryResponse are automatically added to the
> outgoing response. The response will include a list named cl.analytic.<id>,
> where id is specified in the local param.
> *Distributed Search*
> The CollectorFactory also has a method called merge(). This method aggregates
> the results from each of the shards during distributed search. The "default"
> CollectoryFactory implements the default merge logic for merging documents
> from each shard. If you define a different docs collector you can override
> the default merge method to merge documents in accordance with how they are
> collected at the shard level.
> With analytic collectors, you'll need to override the merge method to merge
> the analytic output from the shards. An example of how this works is provided
> in the SumCollectorFactory.
> Each collectorFactory, that is specified in the http parameters, will have
> its merge method applied by the Solr aggregator node.
> *Testing the Patch With Sample Data*
> 1) Apply patch to Solr 4.1
> 2) Load sample data
> 3) Send the http command:
> http://localhost:8983/solr/select?q=*:*&cl=true&facet=true&facet.field=manu_id_s&cl.analytic=%7B!+id=%271%27+groupby=%27manu_id_s%27+column=%27price%27%7Dsum
>
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