mongodb read/write performance and mongo hosting in the cloud

we are currently developing a high traffic rails application with facebooker (facebook game). since amazon simpledb (aws-sdb) is really slow, we are thinking of using a dedicated mongodb server as offered by mongoHQ for example.

questions:

1. what is the read/writes peak value for a mongodb server running on a amazon ec2 instance?
2. what would be a recommended setup for a ec2 hosted app with mongodb - a master on amazon EBS and replicas on the ec2 instances? any examples or experiences?
3. is there a company that offers mongodb hosting in the cloud?

thanks, mz

1) Your reads/inserts/updates values will vary greatly with the size of the EC2 instance you use. A large EC2 instance can perform about 320,000 operations per second. Here is a breakdown of what "operations" meant in that sense:

IIRC, it was ~20,000 each of writes, deletes, updates, inserts, commands, & get mores and ~200,000 reads. I think that it was a quite large data set, but I'll check with Eliot tomorrow. -- Kristina Chodorow

2) MongoDB is single threaded and most EC2 instances have 2 or more CPUs. So you can run two processes on the same machine. Auto-sharding seems to be working well enough in the current release to use in a production environment, but Replica sets are not (these would handle replication & automatic failover). So feel free to use auto-sharding with manual master-slave configurations then replace master-slave config in July when Replica sets are out of alpha.

3) MongoHQ, MongoMachine both offer hosted MongoDB.

MongoDB since 1.4 can very easily saturate a large number of cores. You no longer need to start a mongod per core.