Non-targeted (or scatter/gather) queries can severely hurt the performance of a sharded cluster. Furthermore, scatter/gather queries can be hard to find and debug: enable profiling on a shard's primary (and potentially secondaries), profile every query, runs queries against the system.profile collection to find queries without the shard key.

This becomes more complex when there are tens of sharded collections across multiple databases.

A simple warning message in the mongos logs would help incredibly:

"warning: broadcast query

"