Re: Add mention of execution time memory for enable_partitionwise_* GUCs

Thank you for the patch improving the docs, I think it's a clear
improvement from before.

On Thu, 18 Jul 2024, David Rowley wrote:

> I considered writing about work_mem, but felt I wanted to keep it as
> brief as possible and just have some words that might make someone
> think twice. The details in the work_mem documentation should inform
> the reader that work_mem is per executor node. It likely wouldn't
> hurt to have more documentation around which executor node types can
> use a work_mem, which use work_mem * hash_mem_multiplier and which use
> neither. We tend to not write too much about executor nodes in the
> documents, so I'm not proposing that for this patch.

This is the only part I think is missing, since we now know (measurements
in [1], reproducible scenario in [2]) that the number of partitions plays
an important role in sizing the RAM of the server. It's just too big to
not mention that worst case will be n_partitions * work_mem.

[1] https://www.postgresql.org/message-id/d26e67d3-74bc-60aa-bf24-2a8fb83efe9c%40gmx.net

[2] https://www.postgresql.org/message-id/af6ed790-a5fe-19aa-1141-927595604c01%40gmx.net

I would also like to add an entry about this issue with links to the above
pages, to the TODO page at [3], as this is the only bugtracker I'm aware
of. Am I doing it right bringing it up for approval on this list?

[3] https://wiki.postgresql.org/wiki/Todo

Thanks,
Dimitris