Re: Parameter value from (mb/gb) to bytes

On Wed, Oct 14, 2020 at 5:23 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Magnus Hagander <magnus(at)hagander(dot)net> writes:
> > On Wed, Oct 14, 2020 at 5:10 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> It's fairly annoying that this doesn't work:
> >> regression=# select pg_size_bytes(setting||' '||unit) from pg_settings
> >> where name = 'shared_buffers';
>
> > Actually thinking though, surely *this* particular case can be spelled
> as:
> > SELECT pg_size_bytes(current_setting('shared_buffers'))
>
> Yeah, that might be the most recommendable way.
>
> > Or if doing it off pg_settings:
> > SELECT setting::bigint * pg_size_bytes(unit) from pg_settings where
> > name='shared_buffers'
>
> No, because that will fail for any unit other than '8kB', eg
>
> regression=# select pg_size_bytes('MB');
> ERROR: invalid size: "MB"
>

Right, but it would certainly work for *this* case using pg_asettings, is
what I meant.

That said, I think it'd then actually be better to teach pg_size_bytes to
know that "MB" is the same as "1MB" and parse that. That might be something
that would actually be useful in other cases as well -- basically as a way
to get conversion units in general. Basically if the string is "unit only"
then consider that as "1 unit".

--
Magnus Hagander
Me: https://www.hagander.net/ <http://www.hagander.net/>
Work: https://www.redpill-linpro.com/ <http://www.redpill-linpro.com/>