Since the update to 2.0.x my server (nginx & php-fpm (PHP 5.4.23) seem to throw lots of messages of this kind:
recv() failed (104: Connection reset by peer) while reading response header from upstream
when I try to access piwik. The timeout for the socket connection is set to 120s which should be more than enough. The mysql is on the same server and is accessed directly via localhost.
Additionally, the error.log of php-fpm gives me lots of:
child xxx exited on signal 11 (SIGSEGV) after xxx seconds from start
Problem found! Apc was causing the errors and problems. Disabling apc helped to make everything work without any hiccups.