Re: PostmasterIsAlive() in recovery (non-USE_POST_MASTER_DEATH_SIGNAL builds)

On Thu, Sep 24, 2020 at 05:55:17PM +1200, Thomas Munro wrote:
> Right, RestoreArchivedFile() uses system(), so I guess it can hang
> around for a long time after unexpected postmaster exit on every OS if
> the command waits. To respond to various kinds of important
> interrupts, I suppose that'd ideally use something like
> OpenPipeStream() and a typical WaitLatch() loop with CFI(). I'm not
> sure what our policy is or should be for exiting while we have running
> subprocesses. I guess that is a separate issue.

- if (IsUnderPostmaster && !PostmasterIsAlive())
+ if (IsUnderPostmaster &&
+#ifndef USE_POSTMASTER_DEATH_SIGNAL
+ count++ % 1024 == 0 &&
+#endif
+ !PostmasterIsAlive())
That's pretty hack-ish, still efficient. Could we consider a
different approach like something relying on
PostmasterIsAliveInternal() with repetitive call handling? This may
not be the only place where we care about that, particularly for
non-core code.

No objections with the two changes from pg_usleep() to WaitLatch() so
they could be applied separately first.
--
Michael