mongodb max number of parallel find() requests from single instance

Question

What is the maximum theoretical number of parallel requests that we can squize from single mongodb instance before deciding to shard?

Considering the database and indexes fit in memory and all requests are find() queries fetching single document based on indexed field. The hosting OS is Ubuntu , the data partition is SSD. ulimits are set to max.

In my laptop with simple test on single instance I reach near 40k/sec , after that the avg execution times start to increase significantly, but wondering what can be the upper theoretical limit?

Answer 1

It depends. If your active dataset can fit in the memory - if most of the requests don't need to perform any disk I/O - then you can achieve 24k+ requests pretty easily. If not on a (bigger) single machine, then at least use a replica set cluster with multiple secondaries.

If an active dataset is much larger than the available RAM then you have the same problem as with any other database. The advantage of MongoDB's new engine WiredTiger (since v3.0) is a transparent compression - it can reduce the amount of data and I/O and thus improve performance - even despite the fact that compression adds CPU load.

For more performance it really helps:

• if the most accessed documents are small so it takes less time to load them, transfer them, and less time to deserialize in your app List item
• If you use projections in find(), for the same reasons
• if you use bulk operations to reduce networking I/O and context switches

Even MongoDB itself has an option to limit the maximum number of incoming connections. It defaults to 64k. for more information you can refer link