performance - MongoDB 'count()' is very slow. How do we refine/work around with it?

Question

I am currently using MongoDB with millions of data records. I discovered one thing that's pretty annoying.

When I use 'count()' function with a small number of queried data collection, it's very fast. However, when the queried data collection contains thousand or even millions of data records, the entire system becomes very slow.

I made sure that I have indexed the required fields.

Has anybody encountered an identical thing? How do you do to improve that?

Answer 1

There is now another optimization than create proper index.

db.users.ensureIndex({name:1});
db.users.find({name:"Andrei"}).count();

If you need some counters i suggest to precalculate them whenever it possible. By using atomic $inc operation and not use count({}) at all.

But mongodb guys working hard on mongodb, so, count({}) improvements they are planning in mongodb 2.1 according to jira bug.