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help / color / mirror / Atom feedFrom: Bruce Momjian <[email protected]>
To: [email protected]
To: [email protected]
Subject: Re: Data Type Size Calculation
Date: Mon, 14 Feb 2022 13:51:05 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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 <[email protected]> https://momjian.us
EDB https://enterprisedb.com
If only the physical world exists, free will is an illusion.
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