We are monitoring Memcached servers using the Dynatrace tool, the Memcached is mainly used to store user sessions related data.
- Number of Memcached Servers: 3
- Memory Assigned to each instance: 2 GB
We have recently increased the Memcached memory (from 1 GB to 2 GB) when we had user sessions related issues where users could not Sign In.
We thus increased the Memcached memory for 1 GB to 2 GB. Post increasing we observed a decrease in Eviction rate in the Monitoring tool (Dynatrace)
(There were NO other server/JVM related issues)
My Question: Can I co-relate the User sessions with the Eviction rate? Are there any other parameter/metric that I should look in for Memcached? Is the eviction rate normal 200/s to 400/s normal?
Here is the snap of the Eviction rate and Max bytes for last 72 hours Eviction Rate and Max_bytes
When Dynatrace detects a problem with your user sessions it will also automatically check for anomalies in related metrics.
It is impossible to give a general recommendation on a "good" eviction rate. Focus on the user sessions and the user experience. As long as user experience is OK i wouldn't care about the eviction rate. If you should see problems with user sessions and Dynatrace should also report a relation to anomalies of the eviction rate metric, i can recommend you this article. It explains an interesting relation between the size of objects that are stored in memcached and unexpected evictions.