Datastore API performance tuning

Here's a very interesting benchmarking study about Datastore performance.

http://urbanopus.net/benchmarking-the-ckan-datastore-api/

Note its conclusion about datastore_search

Start by reading the linked benchmarking study, especially its conclusion about datastore_search. No repository file or test is identified, so first locate the datastore_search implementation and its performance tests; the issue is complete only when a specific tuning approach and measurable benchmark improvement are defined.

Written by the indexing model from the issue text.