Re: V4 of PITR performance improvement for 8.4

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.

--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
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