On Fri, Jul 29, 2016 at 8:18 PM, Bruce Momjian <br...@momjian.us> wrote: > The Postgres docs specify that kB is based on 1024 or 2^10: > > https://www.postgresql.org/docs/9.6/static/functions-admin.html > > Note: The units kB, MB, GB and TB used by the functions > pg_size_pretty and pg_size_bytes are defined using powers of 2 rather > than powers of 10, so 1kB is 1024 bytes, 1MB is 10242 = 1048576 bytes, > and so on. > > These prefixes were introduced to GUC variable specification in 2006: > > commit b517e653489f733893d61e7a84c118325394471c > Author: Peter Eisentraut <pete...@gmx.net> > Date: Thu Jul 27 08:30:41 2006 +0000 > > Allow units to be specified with configuration settings. > > and added to postgresql.conf: > > # Memory units: kB = kilobytes Time units: ms = milliseconds > # MB = megabytes s = seconds > # GB = gigabytes min = minutes > # TB = terabytes h = hours > # d = days > > and the units were copied when pg_size_pretty() was implemented. These > units are based on the International System of Units (SI)/metric. > However, the SI system is power-of-10-based, and we just re-purposed > them to be 1024 or 2^10-based. > > However, that is not the end of the story.
Sure it is. The behavior of the code matches the documentation. The documentation describes one of several reasonable behaviors. Full stop. > I am thinking Postgres 10 would be a good time to switch to KB as a > 1024-based prefix. Unfortunately, there is no similar fix for MB, GB, > etc. 'm' is 'milli' so there we never used mB, so in JEDEC and Metric, > MB is ambiguous as 1000-based or 1024-based. I think this would be a backward compatibility break that would probably cause confusion for years. I think we can add new functions that behave differently, but I oppose revising the behavior of the existing functions ... and I *definitely* oppose adding new behavior-changing GUCs. The result of that will surely be chaos. J. Random User: I'm having a problem! Mailing List: Gee, how big are your tables? J. Random User: Here's some pg_size_pretty output. Mailing List: Gosh, we don't know what that means, what do you have this obscure GUC set to? J. Random User: Maybe I'll just give up on SQL and use MongoDB. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers