[ismarc]

It also makes different trade-offs in usability of the software. It is (in my opinion) the most sysadmin friendly datastore, without hiding complexity, the tools are just pleasant to use. However, it has a larger curve for developers. We did a shootout to find a solution that would work for our needs and it came down to Mongo vs. Riak. We went with Mongo and are feeling the pain of getting everything automated and set up, but consider it a one-time cost rather than an "every time we get a new developer" cost.

[wfarr]

Having worked with some quite large Mongo setups, I think you'll find the administration of Mongo ends up being significantly more than a single upfront cost.

Dealing with sharding + replica sets is an administrative nightmare with Mongo.

[mrkurt]

We (MongoHQ) do lots of sharding + replica set admin. Sharding is finicky, but we've found replica set admin to be really straightforward.

Getting client apps configured properly is the hardest part of replica set use. It's only a one time problem though.

[PanMan]

Do you have some more insight into this? We currently run a hybrid Riak-MySQL setup, and are actively looking at Mongo to replace parts of it. In a few tests mongo 's speed seems to be all over the place: From REALLY fast to quite slow. And that is without the admin involved in a larger scale setup.