Re: ToDo: show size of partitioned table

Hi Alvaro,

On 2019/04/03 21:01, Alvaro Herrera wrote:
> On 2019-Apr-03, Kyotaro HORIGUCHI wrote:
>
>> Hello.
>>
>> At Wed, 3 Apr 2019 12:55:06 +0900, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote in <ee892049-0fe4-afe6-cbbf-31cf44fa8522(at)lab(dot)ntt(dot)co(dot)jp>
>>> On 2019/04/03 12:02, Kyotaro HORIGUCHI wrote:
>>>> \dPn doesn't show children because the are of 'r' relkind. And
>>>> \dPn * doesn't show type for children.
>> ...
>>> I think it's intentional that leaf partitions are not shown, because the
>>> patch is meant to allow showing only the "partitioned" members of
>>> partition trees. Regular \d[t|i][+] shows normal tables ('r', 'i', etc.)
>>> including their size, but it's useless for partitioned tables ('P', 'I',
>>> etc.) as far as showing the size is concerned, so the patch. Even \dPn is
>>> meant to only show partitions that are themselves partitioned; note the
>>> "P" in the command.
>>
>> + If the modifier <literal>n</literal> (<quote>nested</quote>) is used,
>> + then non-root partitioned tables are included, and a column is shown
>> + displaying the parent of each partitioned relation.
>>
>> Ah. I see. "non-root *partitined* tables". I misread the
>> phrase. Sorry for the noise.
>
> Well, is this decision an excellent one, from a UI perspective? I was
> surprised by this too and think this should be reconsidered.
>
> I would opt for having \d NOT show partitions at all, myself.

Hmm, in the previous long discussions on this topic, people were opposed
[1] to an idea like this, but maybe they are no longer. Note that the
main opposition came to the idea that \d+ would perform simple
pg_relation_size for regular tables and something else for partitioned
tables, such as, aggregation query over pg_partition_tree.

> When you
> have many partitions (and we're now making the system scale into the
> thousands for a single partitioned table), they clutter the output
> making it unusable. So, rather than think as \dP as "the way to show
> the aggregate size of a partitioned table or index", I'd think it as
> "the way to show detailed info about a partitioned table or index".
> Which includes things like displaying its list of partitions and the
> size of each.

That might be a good idea, but maybe there isn't time left to revise the
proposed patch like that for 12?

Thanks,
Amit

[1]
https://www.postgresql.org/message-id/flat/495cec7e-f8d9-7e13-4807-90dbf4eec4ea(at)lab(dot)ntt(dot)co(dot)jp