From: Tom Lane <tgl@sss.pgh.pa.us>
To: Erik Sjoblom <sjoblom65@gmail.com>
cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Unexpected table size usage for small composite arrays
In-reply-to: <CAAW=00XvzL9q6m2jgsd2YJJqzjjmBYyM3A1uaXuMMr19SpJ57A@mail.gmail.com>
References: <CAAW=00XvzL9q6m2jgsd2YJJqzjjmBYyM3A1uaXuMMr19SpJ57A@mail.gmail.com>
Comments: In-reply-to Erik Sjoblom <sjoblom65@gmail.com>
	message dated "Tue, 22 Oct 2024 17:58:29 -0400"
MIME-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-ID: <2093062.1729636492.1@sss.pgh.pa.us>
Content-Transfer-Encoding: quoted-printable
Date: Tue, 22 Oct 2024 18:34:52 -0400
Message-ID: <2093063.1729636492@sss.pgh.pa.us>
Archived-At: <https://www.postgresql.org/message-id/2093063.1729636492%40sss.pgh.pa.us>
Precedence: bulk

Erik Sjoblom <sjoblom65@gmail.com> writes:
> I=E2=80=99m observing a storage behavior with arrays in a table that dif=
fers from
> my expectations, and I=E2=80=99d appreciate your insights. I was to stor=
e key value
> pairs in a very dense data model. I don't haver the requirement of searc=
h
> so that's why I was thinking an array of a composite type would work wel=
l.
> I can see that padding might be involved using the int4 and int8
> combination but there is more overhead. Anyone know where the following =
it
> coming from?

Composite values use the same 24-byte tuple headers as table rows do.
So you'd be looking at 40 bytes per array element in this example.
A large array of them would probably compress pretty well, but
it's never going to be cheap.

Can you store the int4's and int8's in two parallel arrays?

			regards, tom lane