Re: Minor correction in alter_table.sgml

On 2016/12/01 1:17, Tom Lane wrote:
> Stephen Frost <sfrost(at)snowman(dot)net> writes:
>> Seems like this would be a bit better:
>
>> ------
>> All the actions, when acting on a single table and not using the ALL IN
>> TABLESPACE form, except RENAME and SET SCHEMA, can be combined into a
>> list of multiple alterations to be applied.
>> ------
>
>> I note that we say 'in parallel', but given that we have actual parallel
>> operations now, we should probably shy away from using that except in
>> cases where we actually mean operations utilizing multiple parallel
>> processes.
>
> I follow your beef with use of the word "parallel", but your proposed
> rewording loses the entire point of multiple actions per ALTER TABLE;
> namely that they're accomplished without repeated scans of the table.
>
> Also the above seems a bit clunky; doesn't ALL IN TABLESPACE fall outside
> the restriction "acting on a single table"?
>
> So maybe something like
>
> All the forms of ALTER TABLE that act on a single table,
> except RENAME and SET SCHEMA, can be combined into a
> list of multiple alterations to be applied together.

Updated patch attached.

> We would have to enlarge on what "together" means, but I think there may
> already be text explaining that further down.

There is this explanation:

<para>
The main reason for providing the option to specify multiple changes
in a single <command>ALTER TABLE</> is that multiple table scans or
rewrites can thereby be combined into a single pass over the table.
</para>

Thanks,
Amit