Re: custom function for converting human readable sizes to bytes

On Tue, Dec 29, 2015 at 7:15 PM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
wrote:

>
>> I didn't check out earlier versions of this patch, but the latest one
>> still changes pg_size_pretty() to emit PB suffix.
>>
>> I don't think it is worth it to throw a number of changes together like
>> that. We should focus on adding pg_size_bytes() first and make it
>> compatible with both pg_size_pretty() and existing GUC units: that is
>> support suffixes up to TB and make sure they have the meaning of powers of
>> 2^10, not 10^3. Re-using the table present in guc.c would be a plus.
>>
>> Next, we could think about adding handling of PB suffix on input and
>> output, but I don't see a big problem if that is emitted as 1024TB or the
>> user has to specify it as 1024TB in a GUC or argument to pg_size_bytes():
>> an minor inconvenience only.
>>
>
> Last version still support BP in pg_size_pretty. It isn't big change. PB
> isn't issue.
>
> We have to do significant decision - should to support SI units in
> pg_size_bytes? We cannot to change it later. There is disagreement for SI
> units in pg_size_pretty, so SI units in pg_size_bytes can be inconsistent.
>

There is no way at this point to add support for SI units in a consistent
and backwards-compatible manner: both GUC and pg_size_pretty() use SI
suffixes (kB, MB, GB, TB) with the meaning of 2^(10*n) (KiB, MiB, GiB,
TiB). But given that the size relates to memory or disk space, it is quite
customary *not* to use SI units, so I don't see a point in adding those.

--
Alex