Re: patch to allow disable of WAL recycling

On Wed, Mar 6, 2019 at 11:02 AM Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
wrote:

> On 2019-Mar-06, Robert Haas wrote:
>
> > On Wed, Mar 6, 2019 at 12:13 PM Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
> wrote:
> > > I want your dictating software.
> >
> > I'm afraid this is just me and a keyboard, but sadly for me you're not
> > the first person to accuse me of producing giant walls of text.
>
> Well, I don't have a problem reading long texts; my problem is that I'm
> unable to argue as quickly.
>
> I do buy your argument, though (if reluctantly); in particular I was
> worried to offer a parameter (to turn off zero-filling of segments) that
> would enable dangerous behavior, but then I realized we also have
> fsync=off of which the same thing can be said. So I agree we should
> have two GUCs, properly explained, with a warning where appropriate.
>
> --
> Álvaro Herrera https://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>

It sounds like everyone is in agreement that I should get rid of the
single COW GUC tunable and provide two different tunables instead. I will
update the patch to go back to the original name (wal_recycle) for the
original WAL recycling behavior. The default value of that will be true to
provide the existing behavior. This matches my original proposal from last
year. I will add a new tunable (wal_init_zero) which will control the
zero-fill behavior for the WAL file. Again, the default value will be true
and provide the existing behavior. Both of these could (should) be set to
false for a COW filesystem like ZFS.

If anyone objects to this new approach, let me know, otherwise I'll start
preparing an updated patch.

Thanks for all of the feedback,
Jerry