I think your comment summarizes why this stuff so hard on traditional SQL; one doesn't even know where exactly to start. In MongoDB, you just turn on replication according to http://docs.mongodb.org/manual/replication/, which means basically adding one directive to mongod.conf and typing in the IP addresses of the nodes. MongoDB handles everything else for you. I'm not claiming that it's better or reliabler, just that it's really easy to set it up in 5 minutes.
I would suggest that if you've reached the point where you need streaming replication (rather than, say, a cron job uploading database dumps to s3), you've reached the point where you need to do your research.
You do have a point. PostgreSQL undoubtedly has many more knobs and do you do end up having to learn a fair bit to do stuff like replication.
I'd rather spend more time understanding things up-front and have a reliable solution rather than flick a switch and have something which initially works but I'm not too confident in. That's fine for initial development I suppose, but not in production.
It only takes an hour or so to google and read up on what the different ways of replicating data are in PostgreSQL, their advantages and disadvantages.
I get the feeling that a sizeable proportion of NoSQL users don't have much knowledge of relational databases at all, never mind replication. If you just want to persist some JSON data you already have, I suppose it is quite a large leap to start reading about relational algebra, ACID, undo/redo logs, SQL, and so on.
You've missed the main point of why we use MongoDB. We use it embedded in our product and it's up to our customers to configure HA if they need it. Sure, we document the process for configuring it, but the simpler it is, the less likely a customer is going to have a problem with it.
I would agree with you if it were a database that we maintained in-house, yeah, it's certainly doable. But my main point is that this has to be done in the field at customers who are just trying to use our product.
You are absolutely right, it is as simple as adding the replSet name to your configuration, rs.init(), rs.add() for each other host that will participate in the replica set. Exactly the point.
