Subject: Re: I came here to determine how much storage a boolean variable uses
To: "David G. Johnston" <david.g.johnston@gmail.com>, troy@frericks.us,
 Pg Docs <pgsql-docs@lists.postgresql.org>
References: <163028282061.699.18102158472748913223@wrigleys.postgresql.org>
 <CAKFQuwbjzdq6X0LSPva6GS2PYiBchDdr-bJeOXyuWb87j+7uLw@mail.gmail.com>
From: "Jonathan S. Katz" <jkatz@postgresql.org>
Message-ID: <b5b0eb00-ec60-6c25-b465-67ac2603101e@postgresql.org>
Date: Mon, 30 Aug 2021 12:16:13 -0400
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From: "Jonathan S. Katz" <jkatz@postgresql.org>
To: "David G. Johnston" <david.g.johnston@gmail.com>, troy@frericks.us,
 Pg Docs <pgsql-docs@lists.postgresql.org>
Message-ID: <b5b0eb00-ec60-6c25-b465-67ac2603101e@postgresql.org>
Subject: Re: I came here to determine how much storage a boolean variable uses
References: <163028282061.699.18102158472748913223@wrigleys.postgresql.org>
 <CAKFQuwbjzdq6X0LSPva6GS2PYiBchDdr-bJeOXyuWb87j+7uLw@mail.gmail.com>
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On 8/30/21 11:31 AM, David G. Johnston wrote:
> On Sun, Aug 29, 2021 at 11:59 PM PG Doc comments form
> <noreply@postgresql.org <mailto:noreply@postgresql.org>> wrote:
>=20
>     The following documentation comment has been logged on the website:=

>=20
>     Page: https://www.postgresql.org/docs/13/datatype.html
>     <https://www.postgresql.org/docs/13/datatype.html>
>     Description:
>=20
>     I'd like to see a fourth column added to Table 8-1 that contains th=
e
>     size or
>     size range of the data type.=20
>=20
>=20
> I would argue this is sufficiently provided by the pg_attribute
> catalog's attlen and attalign fields, as pointed to on the same page
> linked below.
>=20
>     Maybe a note about the amount of space in the
>     row that a NULL column uses vs a NOT NULL.
>=20
>=20
> Implementation detail that is covered in the internals section:
>=20
> https://www.postgresql.org/docs/current/storage-page-layout.html#STORAG=
E-TUPLE-LAYOUT
> <https://www.postgresql.org/docs/current/storage-page-layout.html#STORA=
GE-TUPLE-LAYOUT>

Well, it is provided one level deeper in the data type docs, e.g.:

https://www.postgresql.org/docs/13/datatype-boolean.html

I think it's a reasonable request to consider. It potentially duplicates
the info in the data types section (i.e. one more thing to maintain),
but it does provide some convenience for scanning it across the
consolidated table.

Jonathan


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