Re: Row size overhead

Thanks for your reply.

I had used PG 8.3.1 on 32-bit WinXP platform.
"PostgreSQL 8.3.1, compiled by Visual C++ build 1400"
But I suppose this fact doesn't change anything essentially.

Thanks,
Sergey Zubkovsky

-----Original Message-----
From: Pavan Deolasee [mailto:pavan(dot)deolasee(at)gmail(dot)com]
Sent: Wednesday, March 19, 2008 8:23 PM
To: Zubkovsky, Sergey
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: [GENERAL] Row size overhead

2008/3/19 Zubkovsky, Sergey <Sergey(dot)Zubkovsky(at)transas(dot)com>:

>
> Simple calculations show that each row occupies 76 bytes
approximately.
>
> But anticipated row size would be 41 or near.
>

You haven't mentioned PG version. For 8.2 onwards, the tuple header is
23 bytes. Add another 4 bytes for one line pointer for each row. If you
have
null values, another 5 bytes for null bitmap and alignment. Plus add few
bytes
for page header and any unusable space in a page (because a row can not
fit in the remaining space).

Also ISTM that you might be loosing some space because of alignment
in the tuple itself. Try moving booleans and char(3) at the end. There
is not
much you can do with other overheads.

Thanks,
Pavan

--
Pavan Deolasee
EnterpriseDB http://www.enterprisedb.com