Hi, On 2021-12-29 11:31:51 -0800, Andres Freund wrote: > That's pretty much the same - XLogInsert() can trigger an > XLogWrite()/Flush(). > > I think it's a complete no-go to add throttling to these places. It's quite > possible that it'd cause new deadlocks, and it's almost guaranteed to have > unintended consequences (e.g. replication falling back further because > XLogFlush() is being throttled).
I thought of another way to implement this feature. What if we checked the current distance somewhere within XLogInsert(), but only set InterruptPending=true, XLogDelayPending=true. Then in ProcessInterrupts() we check if XLogDelayPending is true and sleep the appropriate time. That way the sleep doesn't happen with important locks held / within a critical section, but we still delay close to where we went over the maximum lag. And the overhead should be fairly minimal. I'm doubtful that implementing the waits on a transactional level provides a meaningful enough amount of control - there's just too much WAL that can be generated within a transaction. Greetings, Andres Freund
