Re: Postgres, fsync, and OSs (specifically linux)

Hi,

On 2018-04-27 19:04:47 -0400, Bruce Momjian wrote:
> On Fri, Apr 27, 2018 at 03:28:42PM -0700, Andres Freund wrote:
> > - We need more aggressive error checking on close(), for ENOSPC and
> > EIO. In both cases afaics we'll have to trigger a crash recovery
> > cycle. It's entirely possible to end up in a loop on NFS etc, but I
> > don't think there's a way around that.
>
> If the no-space or write failures are persistent, as you mentioned
> above, what is the point of going into crash recovery --- why not just
> shut down?

Well, I mentioned that as an alternative in my email. But for one we
don't really have cases where we do that right now, for another we can't
really differentiate between a transient and non-transient state. It's
entirely possible that the admin on the system that ran out of space
fixes things, clearing up the problem.

> Also, since we can't guarantee that we can write any persistent state
> to storage, we have no way of preventing infinite crash recovery
> loops, which, based on inconsistent writes, might make things worse.

How would it make things worse?

> An additional features we have talked about is running some kind of
> notification shell script to inform administrators, similar to
> archive_command. We need this too when sync replication fails.

To me that seems like a feature independent of this thread.

Greetings,

Andres Freund