i have a collection with 10m rows.

this returns in like 10ms:

db.getCollection('people').count()

while this returns like 10s:

db.getCollection('people').aggregate([{$count: 'count'}])

doesn't seem to be related to https://jira.mongodb.org/browse/SERVER-7568, but similar in marked performance diff doing similar ops in aggregation and non-aggregation styles.