On 2019-Mar-06, Robert Haas wrote:
> On Wed, Feb 27, 2019 at 6:12 PM Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> > I think the idea of it being a generic tunable for assorted behavior
> > changes, rather than specific to WAL recycling, is a good one. I'm
> > unsure about your proposed name -- maybe "wal_cow_filesystem" is better?
>
> I *really* dislike this. For one thing, it means that users don't
> have control over the behaviors individually. For another, the
> documentation is now quite imprecise about what the option actually
> does, while expecting users to figure out whether those behaviors are
> acceptable or preferable in their environment. It lists recycling of
> WAL files and zero-filling of those files as examples of behavior
> changes, but it does not say that those are the only changes, or even
> that they are made in all cases.
I can understand this argument. Is there really a reason to change
those two behaviors separately? The reason I wrote the documentation
weasely is that it seems pointless to have to update it whenever we
implement more things controlled by the same GUC option (which we might,
if we learn new things about how to use COW filesystems later on).
AFAIR Jerry's wording was more precise about what the parameter did. If
the only reason to change those behaviors is to make WAL work better on
COW filesystems, then I don't see the point in splitting the GUC in two,
or documenting in minute detail what it does.
That said -- if there *is* such a reason, we can certainly split them up
and indicate to COW-filesystem users to change them both together. I
don't think it's a big deal, but OTOH I see no reason to complicate
matters needlessly.
--
Álvaro Herrera https://www.2ndQuadrant.com/
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