So, today we attempted to migrate object cache from "local file storage" to Redis for our store on Magento EE 18.104.22.168.
After placing the connection details in local.xml and manually clearing var/cache/ on all front-end servers, everything seem to be working well as application performance stayed steady and we could see reads/writes on the Redis DB.
About 40 minutes later, we attempted to flush cache from the admin using the System > Cache Management > Flush Magento Cache button.
From this time on, we saw our application response time double and a large increase in writes to Redis DB. This was not just a brief increase as cache was "re-warmed", response time and Redis DB writes stayed high for 20 minutes until we decided to switch back to local file storage for object cache.
During the period of increased application response time, we manually flushed Redis, but it did not solve the issue.
Can anyone shed any light on why we might have seen this behavior?
Here is a visualization of app response time, showing the effect of switching to Redis for object cache and flushing cache from the admin: