Tried to rollout wmf.21 to group1 wikis, but had a large increase in error rate, more than 10x normal.
Warning: Destructor threw an object exception: exception 'InvalidArgumentException' with message 'LoadBalancer::reuseConnection: connection not found, has the connection been freed already?' in /srv/mediawiki/php-1.28.0-wmf.21/includes/libs/rdbms/loadbalancer/LoadBalancer.php:620
Stack trace:
#0 /srv/mediawiki/php-1.28.0-wmf.21/includes/libs/rdbms/database/DBConnRef.php(599): LoadBalancer->reuseConnection()
#1 (): DBConnRef->__destruct()
#2 {main}