Re: PITR: XLog File compression on Archive

Alvaro Herrera wrote:
> On Mon, Aug 23, 2004 at 10:03:26PM +0100, Simon Riggs wrote:
>
> Simon,
>
> > I raise this now because I'm thinking that this functionality really ought
> > to be in the main production 8.0 release. Not sure if anybody will
> > agree....but that's what I'm thinking now, based upon what seems like a
> > simple design to put it there. My rationale is that it will be simpler to
> > support one file format than two, if we introduce the change at a later
> > time.
>
> Why do you talk about another file format? AFAIU it's the same format,
> only the archived files will lack the page images. Maybe I'm missing
> something?
>
> Anyway I think we are way past feature freeze, and XLog "compression"
> could made it into 8.1 without loss of functionality. At that point we
> will say "now PITR uses less space on the archiver" and that's it.
>
> (Maybe we could even think about LZ-compressing the remaining WAL
> entries on the archived logs?)

Agreed. I added a mention of it in the TODO list:

* Eliminate need to write full pages to WAL before page modification

Currently, to protect against partial disk page writes, we write the
full page images to WAL before they are modified so we can correct any
partial page writes during recovery. These pages can also be
eliminated from point-in-time archive files.

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