Re: Data Type Size Calculation
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(1,100) i;SELECT 100
$ \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
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 wrote:
>
>> On Fri, Feb 11, 2022 at 08:12:08PM +, 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 https://momjian.us
>> EDB https://enterprisedb.com
>>
>> If only the physical world exists, free will is an illusion.
>>
>>
Re: Data Type Size Calculation
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 wrote:
> On Fri, Feb 11, 2022 at 08:12:08PM +, 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 https://momjian.us
> EDB https://enterprisedb.com
>
> If only the physical world exists, free will is an illusion.
>
>
Re: Data Type Size Calculation
On Fri, Feb 11, 2022 at 08:12:08PM +, 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 https://momjian.us
EDB https://enterprisedb.com
If only the physical world exists, free will is an illusion.
