At Tue, 6 Dec 2022 17:23:50 +0530, Bharath Rupireddy <bharath.rupireddyforpostg...@gmail.com> wrote in > Thanks. +1 for fixing this. > > I would like to quote recent discussions on reducing the useless > wakeups or increasing the sleep/hibernation times in various processes > to reduce the power savings [1] [2] [3] [4] [5]. With that in context, > does the archiver need to wake up every 60 sec at all when its latch > gets set (PgArchWakeup()) whenever the server switches to a new WAL > file? What happens if we get rid of PGARCH_AUTOWAKE_INTERVAL and rely > on its latch being set? If required, we can spread PgArchWakeup() to > more places, no?
I thought so first, but archiving may be interrupted for various reasons (disk full I think is the most common one). So, only intentional wakeups aren't sufficient. > Before even answering the above questions, I think we need to see if > there're any cases where a process can miss SetLatch() calls (I don't > have an answer for that). I read a recent Thomas' mail that says something like "should we consider the case latch sets are missed?". It is triggered by SIGURG or SetEvent(). I'm not sure but I believe the former is now reliable and the latter was born reliable. > Or do we want to stick to what the below comment says? > > /* > * There shouldn't be anything for the archiver to do except to wait for a > * signal ... however, the archiver exists to protect our data, so she > * wakes up occasionally to allow herself to be proactive. > */ So I think this is still valid. If we want to eliminate useless wakeups, archiver needs to remember whether the last iteration was fully done or not. But it seems to be a race condition is involved. regards. -- Kyotaro Horiguchi NTT Open Source Software Center
