I spent sometime reviewing/testing the POC. It is relatively simple with a lot of obvious value.
I tested with 16 tables that constantly reach the autovac threashold and the patch did the right thing. I observed concurrent autovacuum workers matching the setting as I was adjusting it dynamically. As you mention above, If there are more autovacs in progress and a new lower setting is applied, we should not take any special action on those autovacuums, and eventually the max number of autovacuum workers will match the setting. I also tested by allowing user connections to reach max_connections, and observed the expected number of autovacuums spinning up and correctly adjusted. Having autovacuum tests ( unless I missed something ) like the above is a good general improvement, but it should not be tied to this. A few comments on the POC patch: 1/ We should emit a log when autovacuum_workers is set higher than the max. 2/ should the name of the restart limit be "reserved_autovacuum_workers"? Regards, Sami Imseih AWS (Amazon Web Services)
