We are using postgres 10, with a setup of master and a hot standby with streaming replication. We use the standby to divide workload of read queries.
We can't find information regarding how hot_standby_feedback will effect the master beside bloating of storage due to delay in cleanup.
Will it have to perform significant work to decide if a query from the standby should delay cleanup?
If I understand it right, the no longer needed by any transaction tuples are not removed unless HOT update or vacuum happens. So master will not have to make any decision, unless one of two happens. thus the overall load should not be affected by hot_standby_feedback much, maybe vacuum will have to do additional ticks probably.
My assumptions are based purely on documentation and experience. I did not look into the source code...
