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Re: Physical column size

From: Mario Weilguni <mweilguni(at)sime(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Cc: Paul Mackay <mackaypaul(at)gmail(dot)com>
Subject: Re: Physical column size
Date: 2006-01-26 11:22:03
Message-ID: 200601261222.03526.mweilguni@sime.com (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-performancepgsql-sql
Am Donnerstag, 26. Januar 2006 11:06 schrieb Paul Mackay:
> Hi,
>
> I've created a table like this :
> CREATE TABLE tmp_A (
> c "char",
> i int4
> );
>
> And another one
> CREATE TABLE tmp_B (
> i int4,
> ii int4
> );
>
> I then inerted a bit more than 19 million rows in each table (exactly the
> same number of rows in each).
>
> The end result is that the physical size on disk used by table tmp_A is
> exactly the same as table tmp_B (as revealed by the pg_relation_size
> function) ! Given that a "char" field is supposed to be 1 byte in size and
> a int4 4 bytes, shouldn't the tmp_A use a smaller disk space ? Or is it
> that any value, whatever the type, requires at least 4 bytes to be stored ?

I think this is caused by alignment.


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