E. How many users were connected when the problem occurred?

About 350 connections

Thanks

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Probably that is your problem, if you don’t have connection pooler.

I’d recommend to start with PgBouncer, very light-weight and easy to configure.

 

Regards,

Igor Neyman

 

I'm building such a system, but I don't think that's the problem because now, with 30 active connections, it still does not work (actually it's extremely slow).

Both servers are far from being under heavy load (so they were before...)