Problem

Currently, if administrators install plugins during a peak period, when many users are active on the instance, it may have severe impact on performance and even accessibility of core functionality.

The reason for this partly is having related caches reset globally, which can be a cascade operation, not only affecting the caches related to the very plugin being upgraded, but others dependent on it. This may have the effect of the instance being locked up for 10+ minutes even, depending on the number of active user sessions and the caches affected

Workaround

Based on the facts above, we suggest not to implement major configuration changes during peak-hours. Make sure to schedule such major changes to off-peak hours (overnight or during weekend), when user activity on the instance is minimal.

Proposed solution

One possible solution would be to block/reject incoming user requests during plugin installation/upgrade, to have the impacted period around 30s instead of minutes.