Re: postgresql storage and performance questions

2007/11/19, Josh Harrison <joshques(at)gmail(dot)com>:
> Hi,
> I have a few questions about the storage and performance
>
> 1. How do you estimate the table size in postgresql?
> For example if I have a table 'Dummy' with 1 varchar (40) & 1
> numeric(22,0) fields and 1000 rows, what is the tablesize estimate for
> this (including the row overhead etc)? How many pages will this
> occupy?
>
> 2. Also if the table contains null columns, does postgres allocates
> the same space for these nulls columns? How does it handle 'nulls' in
> terms of storage?

Try these:
http://www.postgresql.org/docs/current/static/datatype-numeric.html
http://www.postgresql.org/docs/current/static/datatype-character.html
http://www.postgresql.org/docs/current/static/storage-page-layout.html

ad.1 ) There is a fixed-size header (occupying 27 bytes on most
machines) for each tuple

so you will have about 27 + 1 + varchar data + numeric data per row,
plus some overhaed for block headers

ad.2 ) there is a null bitmap for each tuple which has nullable fields
- so every 8 NULLable columns occupy one byte bitmap.

PS. why do you post same thing many times? this is kinda.. spam?

--
Filip Rembiałkowski