Re: POC: Cleaning up orphaned files using undo logs

On Mon, Sep 20, 2021 at 10:24 AM Antonin Houska <ah(at)cybertec(dot)at> wrote:
>
> Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> > On Fri, Sep 17, 2021 at 9:50 PM Dmitry Dolgov <9erthalion6(at)gmail(dot)com> wrote:
> > >
> > > > On Tue, Sep 14, 2021 at 10:51:42AM +0200, Antonin Houska wrote:
> > >
> > > * What happened with the idea of abandoning discard worker for the sake
> > > of simplicity? From what I see limiting everything to foreground undo
> > > could reduce the core of the patch series to the first four patches
> > > (forgetting about test and docs, but I guess it would be enough at
> > > least for the design review), which is already less overwhelming.
> > >
> >
> > I think the discard worker would be required even if we decide to
> > apply all the undo in the foreground. We need to forget/remove the
> > undo of committed transactions as well which we can't remove
> > immediately after the commit.
>
> I think I proposed foreground discarding at some point, but you reminded me
> that the undo may still be needed for some time even after transaction
> commit. Thus the discard worker is indispensable.
>

Right.

> What we can miss, at least for the cleanup of the orphaned files, is the *undo
> worker*. In this patch series the cleanup is handled by the startup process.
>

Okay, I think various people at different point of times has suggested
that idea. I think one thing we might need to consider is what to do
in case of a FATAL error? In case of FATAL error, it won't be
advisable to execute undo immediately, so would we upgrade the error
to PANIC in such cases. I remember vaguely that for clean up of
orphaned files that can happen rarely and someone has suggested
upgrading the error to PANIC in such a case but I don't remember the
exact details.

--
With Regards,
Amit Kapila.