Re: Research/Implementation of Nested Loop Join optimization

Tom Lane escribió:
> Gregory Stark <stark@enterprisedb.com> writes:
> > "Manoel Henrique" <mhenriquesgbd@gmail.com> writes:
> >> Yes, I'm relying on the assumption that backwards scan has the same cost as
> >> forward scan, why shouldn't it?
> 
> > Because hard drives only spin one direction
> 
> Good joke, but to be serious: we expect that forward scans will result
> in the kernel doing read-ahead, which will allow overlapping of
> CPU work to process one page with the I/O to bring in the next page.

I wonder if this is spoiled (or rather, the backwards case fixed) by the
attempts to call posix_fadvise() on certain types of scan.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
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