We were performing numerous queries for every user or review request

being indexed. This led to slowdowns when performing large indexes, or

on slower search backends.
We now make full use of select_related() and prefetch_related(),

iterating over the cached results instead of performing new queries to

filter content.
For 100 users, this should reduce the query count from 201 queries to 3.

For 100 review requests, the query count should be reduced from 402 to

5.

Tested a full search index with queries turned on. Saw that we no longer

had per-item queries, and that all content was being indexed properly.