Re: Practical impediment to supporting multiple SSL libraries

Stephen Frost <sfrost(at)snowman(dot)net> writes:

> Another thought along these lines: Perhaps a 'PQgettuple' which can be
> used to process one tuple at a time. This would be used in an ASYNC
> fashion and libpq just wouldn't read/accept more than a tuple's worth
> each time, which it could do into a fixed area (in general, for a
> variable-length field it could default to an initial size and then only
> grow it when necessary, and grow it larger than the current request by
> some amount to hopefully avoid more malloc/reallocs later).

I know DBD::Oracle uses an interface somewhat like this but more
sophisticated. It provides a buffer and Oracle fills it with as many records
as it can.

It's blocking though (by default) and DBD::Oracle tries to adjust the size of
the buffer to keep the network pipeline full, but if the application is slow
at reading the data then the network buffers fill and it pushes back to the
database which blocks writing.

This is normally a good thing though. One of the main problems with the
current libpq interface is that if you have a very large result set it flows
in as fast as it can and the library buffers it *all*. If you're trying to
avoid forcing the user to eat millions of records at once you don't want to be
buffering them anywhere all at once. You want a constant pipeline of records
streaming out as fast as they can be processed and no faster.

--
greg