Error 422 when load testing Rails 3.1 application with JMeter

I have a Rails 3.1 application that I am trying to use JMeter to load test.

Our site is targeted around collecting information so users sign-up and then walk through a question and answer workflow and after answering a few questions, they are rewarded with some useful information.

My JMeter test is configured to walk through sign-up and then the full Q&A workflow.

Environment details:

RedHat Enterprise 6
Rails 3.1
Ruby 1.9.2p290
DB: Postgres 9

I have run tests with 20 and 100 concurrent threads and a ramp-up time of 1 thread per second and the results are ok. However, as soon as I increase the rampup time so there are multiple threads spawned in a second (even as little as 2 per second), about half of the signup calls fail with an error 422. Once that happens, for those same threads, the Q&A workflow breaks because we are assuming that there is a valid user answering questions.

I'm trying to figure out if there 开发者_如何学编程is a problem with the application code, server configuration, or JMeter setup.

Any thoughts or suggestions on how to troubleshoot this further would be greatly appreciated.

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It may be a cookie issue on the JMeter side wherein non-unique cookies are being assigned to multiple threads.

http://rfc-ref.org/RFC-TEXTS/4028/chapter6.html#d4e441904

This extension introduces the 422 (Session Interval Too Small)
response code. It is generated by a UAS or proxy when a request
contains a Session-Expires header field with a duration below the
minimum timer for the server. The 422 response MUST contain a Min-SE header field with the minimum timer for that server.