Re: Correct use of cursors for very large result sets in Postgres

Thanks, Tom.

Wouldn't this mean that cursors are noticeably non-optimal even for normal
data sizes, since the entire data to be streamed from the table is always
duplicated into another buffer and then streamed?

> if you want the whole query result at once, why are you bothering with a
cursor?

The PostgreSQL docs (
https://www.postgresql.org/docs/9.6/static/plpgsql-cursors.html#AEN66551)
clearly
recommend cursors as a way to return a reference to a large result set from
a function (as I understood, this is recommended precisely as a way to
avoid tuple-based buffering of the data).

So following that advice, it's not unreasonable that I would actually have
a cursor to a large dataset.

Then, I would ideally want to be able to fetch the data from that cursor
without the entire data getting duplicated (even if only a bit at a time
instead of all at once, which seems to be the best case behaviour) as I go.

Additionally, I thought that if I had a streaming use-case (which I do),
and a streaming data-access layer (which I do), then since `SELECT * FROM
large` is absolutely fine, end-to-end, in that situation, then by symmetry
and the principle of least astonishment `FETCH ALL FROM cursor` might be
fine too.