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https://issues.apache.org/jira/browse/SOLR-4465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13606252#comment-13606252
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Erik Hatcher commented on SOLR-4465:
------------------------------------
Joel - nice work!
A few comments:
* Before trying the exact link you provided in the description to a working
example, I tried
http://localhost:8983/solr/select?q=*:*&cl=on&cl.delegating=sum&cl.sum.0.column=price
without specifying cl.topdocs=default and got an error. Maybe if there is no
cl.topdocs specified, it automatically uses the "default"?
* The additional info in the response (<lst name="cl.sum.0"> in this example)
is coming out before/above the results (<result name="response"...>). This
should probably come out after the results to avoid any issues with clients
that are looking for the results in a particular spot (which of course they
shouldn't be, but if we easily move after the results that would be better)
* I'm not fond of the ordinals. Seems like we can do away with them somehow,
leveraging local params. I'm not sure how that would look just yet, and maybe
ordinals is the best way here but it's a new kind of syntax for parameters that
would be nice to avoid if possible.
> 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: 4.3
>
> 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
>
>
> 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.
> You can tell Solr which collectorFactory to use at query time using http
> parameters. All collector parameters start with the prefix "cl".
> 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 Topdocs Collectors*
> You can specify two types of pluggable collectors. The first type is the
> topdocs collector. For example:
> cl.topdocs=<name>
> The above param points to the named collectorFactory in the solrconfig.xml to
> construct the collector. Topdocs collectorFactorys must return collectors
> that extend the TopDocsCollector base class. Topdocs collectors are
> responsible for collecting the doclist.
> You can pass parameters to the topdocs collectors by adding "cl." http
> parameters. By convention you can pass parameters to the topdocs collector
> like this:
> cl.topdocs.max=100
> This parameter will be added to the collector spec because of the "cl."
> prefix and passed to the collectorFactory.
> *Pluggable Custom Analytics With Delegating Collectors*
> You can also specify any number of delegating collectors with the
> "cl.delegating" parameter. Delegating collectors are designed to collect
> something else besides the doclist. Typically this would be some type of
> custom analytic.
> cl.delegating=sum,ave
> The parameter above specifies two delegating collectors named sum and ave.
> Like the topdocs collectors these point to named collectorFactories in the
> solrconfig.xml.
> Delegating collector factories must return Collector instances that extend
> DelegatingCollector.
> A sample delegating 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.
> To communicate with delegating collectors you need to reference the name and
> ordinal of the collector.
> The ordinal refers to the collectors ordinal in the comma separated list.
> For example:
> cl.delegating=sum,ave&cl.sum.0.groupby=field1
> The "cl.sum.0.groupy" parameter tells the "sum" collector at the 0 ordinal to
> group by "field1".
> Delegating 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.
> *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 topdocs collector you can override
> the default merge method to merge documents in accordance with how they are
> collected at the shard level.
> With delegating 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 aggregator.
> *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/collection1/select?q=*%3A*&wt=xml&indent=true&cl=true&cl.topdocs=default&cl.delegating=sum&cl.sum.0.groupby=manu_id_s&cl.sum.0.column=price
> The doclist will be generated by the "default" topdocs collector and the
> output will include a map named "cl.sum.0" which will have output from the
> delegating sum collector.
>
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