Here is major 3.4 -> 4.4 upgrade log:
5159:20191217:143705.304 Starting Zabbix Server. Zabbix 4.4.3 (revision 6cad6f888e).
5159:20191217:143705.304 ****** Enabled features ******
5159:20191217:143705.304 SNMP monitoring: YES
5159:20191217:143705.304 IPMI monitoring: YES
5159:20191217:143705.304 Web monitoring: YES
5159:20191217:143705.304 VMware monitoring: YES
5159:20191217:143705.305 SMTP authentication: YES
5159:20191217:143705.305 ODBC: YES
5159:20191217:143705.305 SSH2 support: YES
5159:20191217:143705.305 IPv6 support: YES
5159:20191217:143705.305 TLS support: YES
5159:20191217:143705.305 using configuration file: /etc/zabbix/zabbix_server.conf
5159:20191217:143705.317 current database version (mandatory/optional): 03050046/03050046
5159:20191217:143705.317 required mandatory version: 04040000
5159:20191217:143705.317 starting automatic database upgrade
5159:20191217:144529.032 completed 100% of database upgrade
5159:20191217:144529.033 database upgrade fully completed
5159:20191217:144538.309 starting event name update forced by database upgrade
5159:20191217:144539.126 completed 1% of event name update
5159:20191217:144732.434 completed 99% of event name update
5159:20191217:144732.823 completed 100% of event name update
5159:20191217:144732.829 event name update completed
5159:20191217:144733.292 server #0 started [main process]
5528:20191217:144733.294 server #1 started [configuration syncer #1]
5529:20191217:144733.294 server #2 started [ipmi manager #1]
5689:20191217:144734.088 server #158 started [preprocessing worker #1]
5661:20191217:144734.299 cannot process proxy "zabbixproxy-01.xxxxx": protocol version 3.4 is not supported anymore
.... normal operations
(ignore initial dbversion 03050046, caused by first failed attempt)
See legend on graphs, history:
Of course it will stay is trends too:
Such numbers may mislead, so zabbix should not calculate such wrong numbers.
Maybe it's caused by specific change in 4.0 - exiting events name update.
But, after the upgrade, I needed to restart zabbix server a few times. And every time after restart, server logs 100% busy spikes for many "internal process busy level" items.
And what possibly would be useful and acceptable - just do NOT collect internal statistic during very first minute after daemon started. I.e start to collect internal statistic after 1 minute.
It probably would be really useful for all the installations!