While upgrading our shard cluster to MongoDB 5.0 we encountered a problem with the primary of the biggest shard consuming a lot of CPU. After we upgraded all the secondaries everything was fine, but when we made one of the upgraded secondaries primary, it started consuming a lot of CPU. So if the primary is 4.4 everything is as usual, but if it’s 5.0 there’s a lot of CPU consumption by it.
I reported this to MongoDB Jira in this ticket
https://jira.mongodb.org/browse/SERVER-71246 and provided the diagnostic data, but unfortunately they couldn’t help me.
And now I don’t know where to look for the solution.
So any advice is appreciated.