Re: segment size depending *_wal_size defaults (was increasing the default WAL segment size)

On 2017-08-30 12:52:26 +0900, Michael Paquier wrote:
> On Wed, Aug 30, 2017 at 11:20 AM, Peter Eisentraut
> <peter(dot)eisentraut(at)2ndquadrant(dot)com> wrote:
> > On 8/29/17 20:36, Andres Freund wrote:
> >> So the question is whether we want {max,min}_wal_size be sized in
> >> multiples of segment sizes or as a proper byte size. I'm leaning
> >> towards the latter.
> >
> > I'm not sure what the question is or what its impact would be.
>
> FWIW, I get the question as: do we want the in-memory values of
> min/max_wal_size to be calculated in MB (which is now the case) or
> just bytes. Andres tends for using bytes.

Not quite. There's essentially two things:

1) Currently the default for {min,max}_wal_size depends on the segment
size. Given that the segment size is about to be configurable, that
seems confusing.
2) Currently wal_segment_size is measured in GUC_UNIT_XBLOCKS, which
requires us to keep two copies of the underlying variable, one in
XBLOCKS one in bytes. I'd rather just have the byte variant.

Regards,

Andres