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/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
