Currently we experience up to 5000 concurrent sessions on a single OX machine in a cluster. It is expectable that all sessions are for user in different contexts. So the groupware process needs to be able to keep that much contexts in the cache.

In the configuration file /opt/open-xchange/etc/groupware/cache.ccf the line
is changed to
jcs.region.Context.cacheattributes.MaxObjects=1000 0
to have enough space in the cache for holding loaded contexts.