Performance issues with 'unique' function in json facets over a high cardinality field

[alexpusch <al...@getjaco.com>]

Hi,
I have a surprising performance issue with the 'unique' function in a json
facet

My setup holds large amount of docs (~1B), despite this large number I only
facet on a small result set of a query, only a few  docs. The query itself
returns as fast as expected, but when I try to do a unique count on one of
the fields using json.facet the query takes much longer. 

Facet time remains constant when I try to do it over a much larger set of
docs. This leads me to believe that this unique count actually depends on
overall field cardinality and not the cardinality in the result set. Am I
right?

This phenomena occurs both in a high level facet, and a sub facet
calculation, which I actually interested in.

Is there a way to facet, and sub-facet over a field with overall high
cardinality, but small cardinality in the result set?

My setup is Solr 6.0 in a Datastax Enterprise cluster

example queries:





Thanks,
Alex



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