[bluesnowmonkey]

At large scale, the queries you can handle are limited by the indexes you have in place, and you can’t index everything. So you already have to think about which queries you’ll really need.

There’s also caching, which is another side of the same coin as indexing. You may want to cache certain common/expensive queries. You’ll probably need to think about the granularity of what gets cached, and how to invalidate it. Hard problems for a dynamic, “query anything” API.

Also you probably need to control which data can be retrieved. KronisLV covered that.