Achim,
Solr can be extended to plugin custom analytics. The code snippet you
mention is part of the framework which enables this.
Here is how you do it:
1) Create a QParserPlugin that returns a Query that extends PostFilter.
2) Then implement the PostFilter api and return a DelegatingCollector that
collects whatever you like.
3) DelegatingCollector.finish() signals your collector that the search has
completed.
4) You can output your analytics directly to the ResponseBuilder. You can
get a reference to the ResponseBuilder through a static call in the
SolrRequestInfo class.
In Solr 4.9 you'll be able to implement your own MergeStrategy, to merge
the results generated by DelegatingCollectors on the shards (SOLR-5973).
The pluggable collectors in that ticket are for ranking. The PostFilter
delegating collectors are a better place for doing custom analytics.
Joel Bernstein
Search Engineer at Heliosearch
On Tue, May 20, 2014 at 6:01 PM, Achim Domma <do...@procoders.net> wrote:
> Hi,
>
> I have a project, where we need to do aggregations over facetted values.
> The stats component is not powerful enough anymore and the new statistic
> component seems not to be ready yet. I understand that it's not easy to
> create a general purpose component for this task. I decided to check
> whether I can solve my use case by myself, but I'm struggling. Any
> clarification regarding the following points would be very appreciated:
>
> - I assume that some of my use cases could be solved by using a custom
> collector. Lucene seems to be build to be extensible by deriving classes
> and overriding methods. That's how I would expect SOLID code to be. But
> looking at the SOLR code, I see a lot of hard coded types and no way to
> just exchange the collector. This is the case for most of the code parts I
> have read, so I wonder: Is there another way to customize / extend SOLR?
> How is the SOLR code supposed to be reused?
>
> - I found several times code snippets like " if (collector instanceof
> DelegatingCollector) { ((DelegatingCollector)collector).finish() } ". Such
> code is considered bad practice in every OO language I know. Do I miss
> something here? Is there a reason why it's solved like this?
>
> cheers,
> Achim
