Gitlab 9.2.2 spams PostgreSQL backend connections


we have a gitlab 9.2.2 installation and using an external postgresql database-server (v9.5.7). The installation runs on an CentOS 7.3 x64 - Server.
Since the update from 8.X.X to 9.X.X we have the problem that gitlab does not release its database connections so the available backend connections are full after a short period of time. Only a restart of gitlab releases the database conncections.
The relevant gitlab configuration looks like:

gitlab_rails[‘db_adapter’] = “postgresql”
gitlab_rails[‘db_encoding’] = “utf8”
gitlab_rails[‘db_database’] = “gitlab”
gitlab_rails[‘db_pool’] = 10
gitlab_rails[‘db_username’] = “XXXXXXXX”
gitlab_rails[‘db_password’] = “XXXXXXXX”
gitlab_rails[‘db_host’] = “pg-standard01-master.tolina.local”
gitlab_rails[‘db_port’] = 5432

Is this a bug or do I have to configure something?