how to deal with race conditions in a RESTful application?

Question

Here is what's happening in my RESTful web app:

1. HTTP request comes in
2. The app starts to build a response, with some initial portion of data
3. Another requests changes the data that where used in step 2
4. The first request understands that the data are expired

What should it do? Fail the request and return an error to a client? Or it should start from scratch (taking more time than the client expects)?

Answer 1

IMHO you should treat a REST request very close to how you treat a DB transaction:

• Either make sure, you lock what to need to lock before doing some real work
• Or prepare to fail/retry on a concurrency issue

Very often this can actually be handed down to a DB transaction - depending on how much and what non-DB work your request does.