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MongoDB Tricks: count() operation

From a ☞ thread on MongoDB group:

count() without a query is an instant O(1) operation.

count({}) with a query is an O(n) operation. Having an index on the query field will speed up the process, but it will still require counting each object. I would suggest keeping real-time counters using $inc where possible to avoid large counts.

There’s also ☞ JIRA ticket marked as fixed in MongoDB 1.7.

Original title and link: MongoDB Tricks: count() operation (NoSQL databases © myNoSQL)