Re: old synchronized scan patch

On Tue, 2006-12-05 at 11:28 +0100, Zeugswetter Andreas ADI SD wrote:
> > To open up the implementation topic:
> >
> > My current patch starts a new sequential scan on a given relation at
> the
> > page of an already-running scan.
>
> I think it should start earlier to make use of the already cached part
> of the table.
> It is hard to determine, or guess how much is still in cache though.
> As a start you could maybe use some (small to be safe) fraction of
> effective_cache_size
> or shared_buffers.

Interesting idea, however it's a little tricky. For instance, we don't
want to start before the oldest cached page, or we have lost the benefit
(just as if we got a bad hint). It also depends on a lot of other parts
of the code, like how scan-resistant the shared buffers are, and how
scan-resistant the OS buffer cache is.

Thoughts?

Regards,
Jeff Davis