Re: Impact of table scan on shared buffers

On Tue, 2007-11-13 at 17:10 -0500, Morris Goldstein wrote:
> I suspect that the SELECT scan will tend to displace everything else
> in shared buffers, and I hope that the two forms of COPY do not. Is
> that correct?
>

In 7.4 that may be true, but in later versions it's not.

8.0+ use multiple LRU lists, and a single access of one block won't
evict a frequently-accessed block from cache. That means some of the
blocks in cache will be displaced, but generally not any
frequently-accessed pages.

In 8.3 (currently in beta), a scan of a table larger than
shared_buffers/4 will have almost no impact on shared buffers.

Regards,
Jeff Davis