I have several tables that I use for logging and real-time stats. These are not critical and since they are a bottleneck I want transactions against them to always be asynchronous. Is there a way to specify this at a table level or do I have to make sure to call set synchronous_commit='off' every time I insert or update to them? And presumably remember to turn it back on again for safety.
There is no clean way to do what you want currently. You have to do the bookkeeping yourself. There was discussion about adding an option for "asynchronous commit" to tables. Then if all the tables changed during a transaction were asynchronous (and a few other conditions were met), the commit would automatically be asynchronous as well. I'd like to see that, but I don't think anyone is actively working on implementing it.