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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?
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Count queries, indexed or otherwise, are slow due to the fact that MongoDB still has to do a full b-tree walk to find the appropriate number of documents that match your criteria.
find({}). count() more fast then collection.
One can identify slow queries in MongoDB by enabling the profiler and configuring it to its some specifications or executing db. currentOp() on a running mongod instance. By looking at the time parameters on the returned result, we can identify which queries are lagging.
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.
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