Thread

Re: [SUPPORT] How to calculate size of tables which are saved on disk?

Pavlo Golub <pavlo.golub@cybertec.at> — 2018-12-05T14:33:53Z

Greetings, Nguyen.

Have you checked https://wiki.postgresql.org/wiki/Disk_Usage ?

You wrote 29.11.2018, 10:40:

> Hello Everyone,


> My name is Thuy.


> This matter is not bug, but I have a question as below. May you help me?
> How to calculate size of tables which are saved on disk?
> Based on my internet searching, how to calculate the length of the table based on the formula:


> 8KB × ceil(number of records / floor(floor(8KB × fillfactor - 24) / (28 + data length of 1 record)))


> Example:
> Column    |     Type      |
> ----------+---------------+
>  aid      | integer       |
>  bid      | integer       |
>  abalance | integer       |
>  filler   | character(84) |
>  


> data length of 1 record = aid(4 bytes) + bid(4 bytes) + abalance(4
> bytes) + filler(84 bytes + 1 byte) = 97 byte
> The data length of a record must be rounded to 8 bytes.
=>> Data length of 1 record is 104 bytes.


> Therefore, I think that 1 character is contained in 1 byte of memory.
> However,  column "filler" can be input with 84 characters "a"
> (single byte) or 84 characters "あ" (double-byte)


> I don’t know why double-byte character can be contained in single byte character?
> Can you explain to me this question?


> Thank you in advance.




-- 
Kind regards,
 Pavlo                          mailto:pavlo.golub@cybertec.at