At CDD we use Selenium RC and spec_selenium to run our acceptance tests. Selenium is a slow way to test in general, but lately for us it's become excruciatingly painful.

For some some unknown reason under Leopard, our tests would seem to randomly slow to a crawl. Tests that usually take 4 seconds to run would suddenly be taking 170+ seconds.

Even worse, this would persist across reboots, and then suddenly go away while we were trying to diagnose the problem.

It was at the point this morning where we were using DTrace to try to figure out what was going on.

Luckily, it doesn't seem to have anything to do with our code, and it looks like I've solved it (or at least worked around it) for now.

Selenium RC communicates over network sockets. It appears that Ruby network communication performance under Leopard is, in a word, terrible.

This problem can be most easily seen when doing a 'gem update' and then waiting forever while the metadata updates.

There seems to be a problem with DNS resolution somewhere in the chain that pops up intermittently.

For now, our workaround is:

  1. Turn off IPv6
  2. Use OpenDNS for lookups.

as suggested by the Ruby Forum thread linked above. That seems to fix things on all of our machines here.

I would file a bug report for this, but I'm not sure if this is a Ruby thing or an OS X thing. If anyone can shed some further light on this issue it would be appreciated.