yum list installed guam
Loaded plugins: product-id, rhnplugin, search-disabled-repos, subscription-manager
This system is receiving updates from RHN Classic or Red Hat Satellite.
guam.x86_64 0.8.3-1.1.el6.kolab_14 @kolab-14-extras-audit
After migration of 56636 mail accounts and setting them productive on sunday 31.07.2016 we awaited the big user storm on monday 01.08.2016 arround 08:00 am and 10:00 am.
After users dripped in from 07:00 am on the response times of simple LIST requests grew up to minutes for just a couple of folders. At some time the system didn't respond any more and guam and cyrus and the clients started to drop sessions and listeners with timeouts and unexpectedly by remote host.
Since we are not abel to read and understand the guam logs we'll send them and the complete maillogs to you to have a look to and maybe find what went wrong here. We stabilized the system after deactivating guam and reconfiguring everything to cyrus. Additionaly we changed the cyrus db format from twoskip to skiplist (due to a bug in cyrus 2.5.8 with twoskip) and changed the "nofiles" to 2000000 on frontend and backend servers.
Here the logs: