On 2017-11-17 11:09:56 +0900, Michael Paquier wrote: > On Fri, Nov 17, 2017 at 10:50 AM, Andres Freund <andres@xxxxxxxxxxx> wrote: > > On 2017-11-06 15:35:03 -0500, Tom Lane wrote: > >> David Pacheco <dap@xxxxxxxxxx> writes: > >> > I ran into what appears to be a deadlock in the logging subsystem. It > >> > looks like what happened was that the syslogger process exited because it > >> > ran out of memory. But before the postmaster got a chance to handle the > >> > SIGCLD to restart it, it handled a SIGUSR1 to start an autovacuum worker. > >> > That also failed, and the postmaster went to log a message about it, but > >> > it's blocked on the pipe that's normally connected to the syslogger, > >> > presumably because the pipe is full because the syslogger is gone and > >> > hasn't read from it. > >> > >> Ugh. > > > > I'm somewhat inclined to say that one has to live with this if the > > system is so resource constrainted that processes barely using memory > > get killed. > > > > We could work around a situation like that if we made postmaster use a > > *different* pipe as stderr than the one we're handing to normal > > backends. If postmaster created a new pipe and closed the read end > > whenever forking a syslogger, we should get EPIPEs when writing after > > syslogger died and could fall back to proper stderr or such. > > I don't have the code on top of my mind, but isn't a custom fd causing > a small penalty Sure, there's some minor overhead because every process would need to close another fd after forking. > when redirection_done is switched to true because the first process > generating a message to the syslogger pipe needs to open it first if > not done yet? I can't follow. The syslogger pipe is created when the first syslogger is started (before it's forked!). Which happens before other processes are created, because they all need to inherit that file descriptor. > So you'd need proper locking to save from race conditions. I completely fail to see why this'd be the case. All I'm talking about is using another pipe between syslogger and postmaster than between other-processes and syslogger. Greetings, Andres Freund -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
