Re: PostgreSQL Limits and lack of documentation about them. - Mailing list pgsql-hackers

From David Rowley
Subject Re: PostgreSQL Limits and lack of documentation about them.
Date
Msg-id CAKJS1f-TEmwnzOELGeaP_2n95eEz1dYWo8eVuZxNyJ10=6DZGQ@mail.gmail.com
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In response to Re: PostgreSQL Limits and lack of documentation about them.  (Peter Eisentraut <peter.eisentraut@2ndquadrant.com>)
List pgsql-hackers
On Thu, 29 Nov 2018 at 07:06, Peter Eisentraut
<peter.eisentraut@2ndquadrant.com> wrote:
>
> That last sentence about the dropped columns is confusing to me:
>
> +    <para>
> +     Columns which have been dropped from the table also contribute to the
> +     maximum column limit, although the dropped column values for newly
> +     created tuples are internally marked as NULL in the tuple's null
> bitmap,
> +     which does occupy space.
> +    </para>
>
> So the dropped columns matter, but they are null, but the nulls matter
> too.  What are we really trying to say here?  Maybe this:
>
> Columns which have been dropped from the table also contribute to the
> maximum column limit.  Moreover, although the dropped column values for
> newly created tuples are internally marked as NULL in the tuple's null
> bitmap, the null bitmap also occupies space.

I'd say that's a small improvement that's worth making.  I've attached
a patch using your reformed version of that paragraph.

-- 
 David Rowley                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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