https://www.depesz.com/2022/02/13/how-much-disk-space-you-can-save-by-using-int4-int-instead-of-int8-bigint/
Hope this link is useful. create table testb as select 'true'::bool as b from generate_series(1,1000000) i;SELECT 1000000 $ \dt+ testb List of relations Schema │ Name │ Type │ Owner │ Persistence │ Access method │ Size │ Description ────────┼───────┼───────┼────────┼─────────────┼───────────────┼───────┼───────────── public │ testb │ table │ depesz │ permanent │ heap │ 35 MB │ Why is that, though? From what I gather the answer is: performance. I don't > know low-level details, but based on what I understand, processors process > data in arch-dependent block sizes. 64bit processor works on 64 bits. And > this means that if you want to do something on int4 value, that is part of > 8 byte block, you have to add operation to zero the other 32 bits. > On Wed, Feb 16, 2022 at 12:26 AM Troy Frericks <troy.freri...@gmail.com> wrote: > For now, yes... I'm suggesting that the documentation be completed by > adding a few sentences few extra sentences. > Troy. > # > > > On Mon, Feb 14, 2022, 12:51 Bruce Momjian <br...@momjian.us> wrote: > >> On Fri, Feb 11, 2022 at 08:12:08PM +0000, PG Doc comments form wrote: >> > The following documentation comment has been logged on the website: >> > >> > Page: https://www.postgresql.org/docs/13/datatype-numeric.html >> > Description: >> > >> > > The actual storage requirement is two bytes for each group of four >> decimal >> > digits, plus three to eight bytes overhead. >> > >> > Please describe what 'overhead' means. >> > >> > I'd like to be able to calculate the data size of NUMBER(19,4). I can >> > calculate 2 bytes per 4 digits... with 19 digits, I have 5 groups of 4 >> > digits, >> > >> > so the data length I seek is 5 bytes + overhead... then I'm left >> hanging. >> > :( >> >> Well, you can create it and then call pg_column_size(): >> >> CREATE TABLE test (x NUMERIC(19,4)); >> >> SELECT pg_column_size('test.x'); >> pg_column_size >> ---------------- >> 7 >> >> If you want more details, you will need to look at the source code. >> >> -- >> Bruce Momjian <br...@momjian.us> https://momjian.us >> EDB https://enterprisedb.com >> >> If only the physical world exists, free will is an illusion. >> >>