Re: Initial prefetch performance testing

On Mon, 2008-09-22 at 04:57 -0400, Greg Smith wrote:

> -As Greg Stark suggested, the larger the spindle count the larger the 
> speedup, and the larger the prefetch size that might make sense.  His 
> suggestion to model the user GUC as "effective_spindle_count" looks like a 
> good one.  The sequential scan fadvise implementation patch submitted uses 
> the earlier preread_pages name for that parameter, which I agree seems 
> less friendly.

Good news about the testing.

I'd prefer to set this as a tablespace level storage parameter. Since
that is where it would need to live when we have multiple tablespaces.
Specifically as a storage parameter, so we have same syntax for
table-level and tablespace-level storage parameters. That would also
allow us to have tablespace-level defaults for table-level settings.

prefetch_... is a much better name since its an existing industry term.
I'm not in favour of introducing the concept of spindles, since I can
almost hear the questions about ramdisks and memory-based storage. Plus
I don't ever want to discover that the best setting for
effective_spindles is 7 (or 5) when I have 6 disks because of some
technology shift or postgres behaviour change in the future.

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Training, Services and Support