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

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.

performance mongodb count

You can ensure that the index is really used without any disk access.

Let's say you want to count records with name : "Andrei"

You ensure index on name (as you've done)and

db.users.find({name:"andrei"}, {_id:0, name:1}).count()

you can check that it is the fastest way to count (except with precomputing) by checking if

db.users.find({name:"andrei"}, {_id:0, name:1}).explain()

displays a index_only field set to true.

This trick will ensure that your query will retrieve records only from ram (index) and not from disk.

performance mongodb count

For me the solution was change index to sparse.It depend on specific situation, just give it a try if you can.

db.Account.createIndex( { "date_checked_1": 1 }, { sparse: true } )db.Account.find({         "dateChecked" : { $exists : true }    }).count()

318 thousands records in collection

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