| From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Gregory Stark <stark(at)enterprisedb(dot)com>, Manoel Henrique <mhenriquesgbd(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Research/Implementation of Nested Loop Join optimization |
| Date: | 2008-07-26 00:37:25 |
| Message-ID: | 20080726003725.GT9891@alvh.no-ip.org |
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| Thread: | |
| Lists: | pgsql-hackers |
Tom Lane escribió:
> Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> > "Manoel Henrique" <mhenriquesgbd(at)gmail(dot)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
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