Re: Add per-backend lock statistics

Hi Bertrand-san,

Thanks for the explanation!

> I think that flushing statistics within running transactions [1] could
help to
> see what's going on for parallel workers too.

Thanks, I'll follow that thread.

> For parallel workers this window
> is very short (between the flush and the exit) so that we can say that
their stats
> are not visible in practice.

> That said, I'm not sure the doc needs any clarifications given that those
functions
> take a PID as parameter and that they state something like "Returns I/O
> /WAL statistics about the backend with the specified process ID".

Right, it's per-PID, and that part is clear. My concern is that it isn't
obvious from the function description that a single query can span more
than one PID, as it does with parallel workers.
If it's worth documenting, I agree splitting it across lock / I/O / WAL
separately isn't great -- a single place such as "Statistics Functions"
seems better. Either way it's separate from this patch, so I'll start a
dedicated thread with a draft.

> It's not related to this thread so that might be worth a dedicated one
but I'm
> not sure that would be more actionable while consuming more resources.

Thanks -- agreed there's a tradeoff here. I can see a use case for it, so
I'd like to weigh that against the cost and, if it still looks worth it,
post it as a separate patch to get more opinions.

No need to reflect either of these in the current patch.

Regards,
Tatsuya Kawata