Re: database physical storage

On Thu, Jun 15, 2006 at 10:26:59AM +0530, Praveen Kumar N wrote:
> I have observed that the size of data (for example size of
> table in a database) stored by database system on physical storage is
> more than actual datasize.It seems database is storing data in some
> format.For example i have created a table with data 15MB considering each
> INTEGER of 4bytes.But after loading this data into database i have
> observed that database system is storing this table in 45MB memory.So can
> anybody tell me what is the reason to use so much memory? Is there any
> relation between actual dataset size and size of data stored on physical
> storage system.

Each row has storage overhead such as values that determine which
transactions can see the row. If rows have only a small amount of
data then the overhead is a large proportion of the storage space.
If a table has indexes then there's even more overhead. For more
information see the "Database Physical Storage" chapter in the
documentation, in particular the "Database Page Layout" section:

http://www.postgresql.org/docs/8.1/interactive/storage-page-layout.html

--
Michael Fuhr