Greetings,
* Michael Paquier (michael@paquier.xyz) wrote:
> On Tue, Nov 27, 2018 at 07:18:39PM -0500, Tom Lane wrote:
> > * When wal_compression is enabled and a "hole" is removed from a full
> > * page image, the page image is compressed using PGLZ compression.
> >
> > (BTW, is this trying to say that we don't apply compression if the page
> > contains no hole? If so, why not?)
>
> Compression can be applied on a page with or without a hole. What this
> sentence means is that the equivalent of a double level of compression
> can be applied on top of the hole being removed, if the hole can be
> removed.
That isn't at all what I got from that.
A rewrite of this really should avoid talking about removing the hole as
if it's 'compression' because, first of all, it isn't, and second, now
that we have *actual* compression happening, it's terribly confusing to
talk about removing the hole using that terminology.
Thanks!
Stephen