From: Ragnar <gnari@hive.is>
To: Paul Mackay <mackaypaul@gmail.com>
Cc: pgsql-general@postgresql.org
Subject: Re: Physical column size
Date: Fri, 03 Mar 2006 10:27:59 +0000
Message-ID: <1141381679.18656.141.camel@localhost.localdomain> (raw)
In-Reply-To: <786c2f6d0603030203m3b7c62a1k6950ceca066dc5ce@mail.gmail.com>
References: <786c2f6d0601260206k2201a548p48af7c7fc085d3b2@mail.gmail.com>
<786c2f6d0603030203m3b7c62a1k6950ceca066dc5ce@mail.gmail.com>
On fös, 2006-03-03 at 11:03 +0100, Paul Mackay wrote:
> 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 inserted 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 ?
the int4 needs to be aligned at 4 bytes boundaries,
making wasted space after the char.
this would probably be the same size:
CREATE TABLE tmp_C (
c "char",
cc "char",
i int4
);
and this would be smaller:
CREATE TABLE tmp_D (
c "char",
cc "char",
ccc "char",
);
P.S.: I did not actually check to
see if the "char" type needs to be aligned,
by I assumed not.
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To: pgsql-sql@postgresql.org
Cc: gnari@hive.is, mackaypaul@gmail.com, pgsql-general@postgresql.org
Subject: Re: Physical column size
In-Reply-To: <1141381679.18656.141.camel@localhost.localdomain>
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