Re: custom function for converting human readable sizes to bytes - Mailing list pgsql-hackers

From Shulgin, Oleksandr
Subject Re: custom function for converting human readable sizes to bytes
Date
Msg-id CACACo5TgZJWj+C570wBVzYT1qCSeCKHtpTi4UN8qZJuVupuLVQ@mail.gmail.com
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In response to Re: custom function for converting human readable sizes to bytes  (Pavel Stehule <pavel.stehule@gmail.com>)
List pgsql-hackers
On Tue, Dec 29, 2015 at 7:15 PM, Pavel Stehule <pavel.stehule@gmail.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

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