Strange Thread related errors

Michael Guterl mguterl at
Thu Jan 7 13:49:52 EST 2010

On Thu, Jan 7, 2010 at 11:31 AM, Iñaki Baz Castillo <ibc at> wrote:
> El Jueves, 7 de Enero de 2010, Michael Guterl escribió:
>> Our Rails app has started raising exceptions (caught by hoptoad
>> thankfully) and I can only imagine they're related to unicorn.  I only
>> think the errors are occurring on the request after we deploy, which
>> upgrades the Unicorn process.  I say this because the errors are
>> coming from many different actions, but I haven't been able to
>> reproduce.
> Let me explain a problem I had with Sequel and Unicorn (already solved),
> perhaps it's related:
> I load Sequel database toolkit in the master process so it generates its own
> threads pool.
> Then Unicorn forks into workers but each worker uses the same instance of
> Sequel database, this is, the same threads pool.
> This causes errors since some thread could be used by different processes at
> the same time.
> The solution is simple:
> Don't set the Sequel instance in the master process, instead do it in each
> worker ("after_fork" block in unicorn config file).
> In this way each process has its own Sequel instance with its own threads
> pool.
> Also, using Sequel thread pool makes no sense when using Unicorn as each
> worker is single thread, so I gain some performance by setting
> "single_threaded = true" in Sequel database configuration (no thread pool
> stuff).
> Probably you are getting a similar issue due to ActiveRecord or any other
> multithread library you load in the master process so the instance is shared
> between all the workers.

We currently disconnect from both databases in before_fork and
re-establish the connection in after_fork.

Here's our unicorn config:

Maybe I should disable connection pooling?

Best regards,
Michael Guterl

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