Hi,
It's simply because we should not refer to system catalog during the recovery.
2009/1/25 Gregory Stark <stark@enterprisedb.com>:
>
> Koichi Suzuki <koichi.szk@gmail.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.
>
> --
> Gregory Stark
> EnterpriseDB http://www.enterprisedb.com
> Ask me about EnterpriseDB's On-Demand Production Tuning
>
--
------
Koichi Suzuki
