Re: 9.6 and fsync=off

Hi,

On 2016-05-02 10:07:50 -0400, Robert Haas wrote:
> I also think that it would be a swell idea to detect whether a system
> has ever crashed with fsync=off, and do something about that, like
> maybe bleat on every subsequent startup for the lifetime of the
> cluster. I think Andres may have even proposed a patch for this sort
> of thing before, although I don't remember for sure and I think he and
> I disagreed on the details. Sketch:

Hm, I can't remember doing that.

> - Keep a copy of the fsync status in pg_control.
> - If we ever enter recovery while it's turned off, say:
> WARNING: Entering recovery with fsync=off; this cluster may be
> irretrievably corrupted.
> ...and also set a separate flag indicating that we've done at least
> one recovery with fsync=off.
> - If that flag is set on a subsequent startup, say:
> WARNING: Recovery was previously performed with fsync=off; this
> cluster may be irretrievably corrupted.

Well, the problem with that is that postgres crashes are actually
harmless with regard to fsync=on/off. It's just OS crashes that are a
problem. So it seems quite likely that the false-positive rate here
would be high enough, to make people ignore it.

Andres