If u need only 200 results grouped, u can easily do it with some external
code, it will be much faster anyway.
Also, it's widely suggested to use docValues="true" for fields, by which
group is performed, it really helps (I can only say numbers in terms of RAM
usage, but speed increases as-well).
You should look at CollapsinQParserPlugin. It's much faster compared to a
Grouping query.
https://wiki.apache.org/solr/CollapsingQParserPlugin
It has a limitation though, check the following JIRA if it might affect your
use-case.
https://issues.apache.org/jira/browse/SOLR-6143
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