Re: Different compression methods for FPI

On Tue, Jun 15, 2021 at 07:53:26AM +0200, Peter Eisentraut wrote:
> On 15.06.21 07:37, Michael Paquier wrote:
> > > > Actually, I was just thinking that default yes/no/on/off stuff maybe should be
> > > > defined to mean "lz4" rather than meaning pglz for "backwards compatibility".
> > > +1
> > I am not sure that we have any reasons to be that aggressive about
> > this one either, and this would mean that wal_compression=on implies a
> > different method depending on the build options. I would just stick
> > with the past, careful practice that we have to use a default
> > backward-compatible value as default, while being able to use a new
> > option.

You're right, I hadn't though this through all the way.
There's precedent if the default is non-static (wal_sync_method).

But I think yes/on/true/1 should be a compatibility alias for a static thing,
and then the only option is pglz.

Of course, changing the default to LZ4 is still a possibility.

> If we think this new thing is strictly better than the old thing, then why
> not make it the default. What would be the gain from sticking to the old
> default?
>
> The point that the default would depend on build options is a valid one.
> I'm not sure whether it's important enough by itself.