ease of scaling mongodb vs mysql

I am creating a Grails application t开发者_如何转开发hat is the backend for a mobile application. It is currently deployed on Amazon EC2. It persists data to a mysql database. One instance currently pointing to the database. I plan to deploy multiple instances of the app behind a load balancer and eventually have read requests go to slave instances of the db. We plan to release in the coming months and have a beta group of a couple of thousand users. It is more read intensive than write.

We have looked into using mongodb instead of sql and see it as a good solution.

Not having a lot of experience scaling mysql ( or mongodb ) would it be easier to scale mongodb since it has features such as auto sharding. ( Looking for thoughts from people who have done both ) I am of thinking it will be easier to switch to mongodb now rather than be in 'production' and having to migrate.

Thoughts?

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MongoDB has two versions of "scaling":

1. Read scaling via replica sets.
2. Write scaling via sharding.

They're not silver bullets, but they're both very easy to set up. Replica sets have auto-failover which is practically essential when using EC2 (they have a good history of just randomly failing nodes). When you need write scaling, MongoDB has documented processes for upgrading your replica set to a series of sharded replica sets.

The unfortunate limitation is that (last I checked), things like scalr don't really support automatic scaling. So you'll have to roll your own solution for adding and removing nodes from the set.

Some important considerations:

1. Disk IO performance is sketchy in the cloud. Good performance is all about the amount of RAM you can throw at the problem.
2. If you're using replica sets for reads, ensure that your driver / data wrapper is capable of handling the distribution of reads. Just like MySQL it's not currently "free", you'll need to decide "write vs. read".
3. 64-bit machines. MongoDB really wants to operate on 64-bit hardware. This is a cost consdieration as you'll probably have to ramp up with 4GB machines instead of 2GB machines (I don't think this is a big limitation, but I also know what it's like to be a startup).
4. MongoDB is still new tech. The lists are very active, and people are using it in production for very large data sets. But this is still a new product, you have to be prepared to work from the command-line and parse through docs and ask questions.

would it be easier to scale mongodb

At some level scaling is going to be a "hard" problem. What MongoDB does well is provide a way to really scale out lots of boxes horizontally with replication. In my experience, MySQL really tops out at around two boxes for writes. You can easily configure co-masters, but after that you have to start mucking around with all kinds of partitioning and you basically lose the ability to do joins.

I am of thinking it will be easier to switch to mongodb now rather than be in 'production'

It probably will.

Thoughts?

Start small. Get one piece working and see if you like how it works. If you have access to an EC2 account, then it's easy to spin up a couple of machines and play. MongoDB is not a panacea, but it works really well for a lot of modern web problems. Just measure how badly you need joins :)