An interesting problem came up today.
One of our models is serializing an arbitrary hash.
This was all well and good until we started looking at runtimes in our controller actions. 34% of runtime was spent parsing YAML.
Experimenting a little, I ran the following test which revealed that JSON.load is two orders of magnitude faster than YAML.load at simple hashes.
This was a shocking result to me, but as I thought about it I realized that YAML exists to store more than just simple hashes, whereas that is all that JSON can do.
It would seem that switching data over from the default YAML to JSON is quite simple.
The problem comes when you have existing data YAML encoded.
I fixed this with a rake task which creates a fake model to avoid other model configurations, validations and automagics and simple parses the YAML and encodes it to JSON. It may not be necessary to create the fake model in the general case, however in my situation where my model is very complicated and doing many different things it was easier to simply eliminate everything.