COW friendly GC and PostgreSQL

Jeremy Evans jeremyevans0 at
Wed Nov 30 15:54:37 EST 2011

On Wed, Nov 30, 2011 at 7:24 AM, Laas Toom <laas.toom at> wrote:
> Hello,
> I stumbled upon a weird issue when upgrading a Rails app and trying to run in on Unicorn!:
> The problem manifested itself via a few different error messages as if garbage/nil was returned from database instead of actual data and it only happened with more than one concurrent request (i.e under load test).
> This turned out to be an issue with COW-friendly GC that I had enabled (taken from the example unicorn.conf). Removing this from unicorn.conf made the app run smooth again.
> Is this something known or did I do something wrong?

If you didn't disconnect the database connection before forking, that
could be the cause of the problem, though you should have issues
regardless of whether the GC is CoW or not.  Did you just turn off
CoW, or did you turn off preload_app as well?

Looking at your config file, try adding a before_fork callback that
disconnects the database connection and things may work fine.


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