---
upgrade:
  - |
    The default value of ``max_overflow`` config option
    has been increased from 10 to 50 in order to allow
    OpenStack services heavily using DBs to better handle
    spikes of concurrent requests and lower the probability
    of getting a pool timeout issue.

    This change potentially leads to increasing of the number
    of open connections to an RDBMS server. Depending on the
    configuration, you may see "too many connections" errors
    in logs of OpenStack services / RDBMS server. The max limit of
    connections can be set by the means of these config options:

    http://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_max_connections
    http://www.postgresql.org/docs/current/static/runtime-config-connection.html#GUC-MAX-CONNECTIONS

    For details, please see the following LP:

    https://bugs.launchpad.net/oslo.db/+bug/1535375

    and the ML thread:

    http://lists.openstack.org/pipermail/openstack-dev/2015-December/082717.html