1. Original report via GitHub: https://github.com/mongodb/mongoid/discussions/5846

"Hello. I've been trying to upgrade the application Mongoid version in my current Job to the latest release available version 7x. We're planning to go through each minor release in order.

"When we upgraded from Mongoid 7.1.11 to 7.2.6, it was noticed a huge performance issue with our application response time. Fortunately, it was possible to roll back to the previous version. While investigating, we did not notice any obvious issues. I researched and looked for similar cases as ours, but could not find any. The only discussion I've found about a performance issue was this one: #5783.

"The response time from our application has gone from a mean of ~3.5s to ~12s with spikes up to ~16s! ...

"So looking at our profiling tool, it seems that it was a general degradation of performance. Every one of our controller actions that use Mongoid models became at least twice slower, especially the ones with embedded objects related. I've run a few simple benchmarks on the Rails console to confirm this..."

NOTE: the reporter says they see the same performance degradation on the latest 7.5.4 release, as well.

See the GitHub discussion for full details, including graphs and benchmarks: https://github.com/mongodb/mongoid/discussions/5846