Re: docs should mention that max_wal_size default depends on WAL segment size

Hi,

On 2018-11-18 22:16:12 +0100, Tomas Vondra wrote:
> while investigating something on a cluster with a non-default WAL
> segment (say 256MB), I've noticed a somewhat surprising behavior of
> max_wal_size default. While the docs claim the default is 1GB, the
> actual default depends on the WAL segment size.
>
> For example with the 256MB WAL segments, you end up with this:
>
> test=# show max_wal_size ;
> max_wal_size
> --------------
> 16GB
> (1 row)
>
> This behavior is not entirely new - I've noticed it on 10, before the
> WAL segment size was moved to initdb (which made it more likely to be
> used). It's even more surprising there, because it leaves
>
> #max_wal_size = 1GB
>
> in the sample config, while fc49e24f at least emits the actual value.
>
> But I'd say not mentioning this behavior in the docs is a bug.

Hm, you're not wrong there. Wonder if it'd be better to make it so that
the default actually has the effect of being 1GB - I think that ought to
be doable?

Greetings,

Andres Freund