Re: Fails to work on live images due to fsync() on pg_commit_ts before doing any write there

On 2017-11-07 16:23:21 +0100, Raphael Hertzog wrote:
> On Tue, 07 Nov 2017, Tom Lane wrote:
> > Yeah, it does sound more like a filesystem bug than anything else.
> > (I completely reject the notion that it's an application error to
> > fsync a directory when you haven't modified it.)
> >
> > In view of the fact that we just wrapped 10.1, it'd be 3 months before
> > any change from our side would reach the wild. I think a key question
> > here is whether the Kali developers are likely to fix it from their side
> > in less time than that.
>
> Fix what?
>
> Following your logic, if anything needs to be fixed, it's the Linux kernel
> that has to be fixed, and in particular its overlayfs filesystem.

Right. The kernel knows the file/directory ain't dirty. We don't.

> The time
> to get a fix there is also relatively long. If they work on a fix quickly,
> it might get merged for Linux 3.15 which we will not have in Kali before
> 2-3 months too.

So the same timeframe as a new PG release?

> For now, I have added an ugly work-around that creates a file in the
> pg_commit_ts directory (and immediately drops it) just before starting
> PostgreSQL:
> http://git.kali.org/gitweb/?p=packages/kali-defaults.git;a=commitdiff;h=f4287fd774f8d0686ba919f57355215a6b9633e3

Hm. The comment:
+ # Ensure the directory is copied over in the tmpfs
suggests that the overlay isn't persistent? If that's indeed the case,
you could just disable fsyncs alltogether.

Greetings,

Andres Freund