Re: Using ProcSignal to get memory context stats from a running backend

Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2017-12-12 11:57:41 +0800, Craig Ringer wrote:
>> TL;DR: Lets add a ProcSignalReason that makes a backend
>> call MemoryContextStats when it sees it and a C func that users can use to
>> set it on a proc. Sane?

> It's not unproblematic. procsignal_sigusr1_handler() runs in a signal
> handler, so you can't really rely on a lot of stuff being legal to do.

Indeed, calling MemoryContextStats in a signal handler would be a damfool
idea, but Craig didn't propose that AFAICS.

> Another question is whether printing to stderr, bypassing proper
> logging!, is good enough for something like this.

Yeah, this is an issue. MemoryContextStats is designed to print
to stderr in the (possibly vain) hope that it will work even when
we are up against an OOM failure. That's not a property I much
want to give up, but you're right that it's not very desirable
if a user is trying to capture state during normal running.

regards, tom lane