Re: [POC] FETCH limited by bytes.

Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp> writes:
> Hello, as the discuttion on async fetching on postgres_fdw, FETCH
> with data-size limitation would be useful to get memory usage
> stability of postgres_fdw.

> Is such a feature and syntax could be allowed to be added?

This seems like a lot of work, and frankly an incredibly ugly API,
for a benefit that is entirely hypothetical.  Have you got numbers
showing any actual performance win for postgres_fdw?

Even if we wanted to do something like this, I strongly object to
measuring size by heap_compute_data_size.  That's not a number that users
would normally have any direct knowledge of; nor does it have anything
at all to do with the claimed use-case, where what you'd really need to
measure is bytes transmitted down the wire.  (The difference is not small:
for instance, toasted values would likely still be toasted at the point
where you're measuring.)
        regards, tom lane