Date: Tue, 15 Jun 2021 11:14:56 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Cc: Michael Paquier <michael@paquier.xyz>,
	Heikki Linnakangas <hlinnaka@iki.fi>,
	Andrey Borodin <x4mmm@yandex-team.ru>, pgsql-hackers@postgresql.org,
	Thomas Munro <thomas.munro@gmail.com>, Peter Geoghegan <pg@bowt.ie>,
	Andres Freund <andres@anarazel.de>
Subject: Re: Different compression methods for FPI
Message-ID: <20210615161456.GP31772@telsasoft.com>
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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.