Re: BUG #19391: pg_ctl: the PID file "/xxxx/postmaster.pid" is empty

PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
> My test framework uses "pg_ctl status ..." to detect a state of Postgres
> instance - uninitialized, stopped, running.
> Time from time, it returns the error - pg_ctl: the PID file
> "/xxxx/postmaster.pid" is empty

If you're issuing "pg_ctl status" while a postmaster is starting, it's
possible that you're hitting the tiny window where CreateLockFile()
has opened the file but not yet written anything into it.

We could imagine making pg_ctl not treat this as an error, but
I'm hesitant to do so because of possibly creating race conditions
for the pg_ctl start/stop cases. (Well, it's inherently a race
situation if you issue two concurrent starts ... what I mean is
that failing is the safest option in that scenario.) Depending
on what you intend to do with the pg_ctl status result, acting
as if this isn't an error case could be risky there too.
Given an empty file, we can't distinguish "a postmaster is in
progress of starting" from "a postmaster died while starting",
since no PID is available to test.

regards, tom lane