Re: V4 of PITR performance improvement for 8.4

On Sun, Jan 25, 2009 at 7:15 AM, Gregory Stark <stark(at)enterprisedb(dot)com> wrote:
> Koichi Suzuki <koichi(dot)szk(at)gmail(dot)com> writes:
>
>> Please find enclosed 2nd patch of pg_readahead which include a patch
>> to bufer manager to skip prefetch of pages already in shared buffer.
>
> I'm a bit confused by this comment. PrefetchBuffer already checks if the page
> is in shared buffers.
>
> What is tricky to avoid is prefetching the same page twice -- since the first
> prefetch doesn't actually put it in shared buffers there's no way to avoid
> prefetching it again unless you keep some kind of hash of recently prefetched
> buffers.
>
> For the index scan case I'm debating about whether to add such a cache
> directly to PrefetchBuffer -- in which case it would remember if some other
> scan prefetched the same buffer -- or to keep it in the index scan code.

Has this issue been resolved? Does this patch need more review?
Because if so, I'm guessing it needs to happen RSN.

...Robert