Re: Initial prefetch performance testing

On Sep 22, 2008, at 12:02 PM, Simon Riggs wrote:

>
> 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.

absolutely; we made tests and got similar figures.
also, I/O is much more stable and steady with the patch.

>
> 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.
>

+1

> 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.

i would definitely avoid to use of "spindles".
i totally agree with simon here. once mature SSD storage or some in-
memory stuff will be available for the masses, this is not suitable
anymore.
the best thing would be to simply use the parameter as it was in the
original patch.
maybe we should simply make the parameter adjustable per table and per
index. this would automatically cover 95% of all cases such as
clustered tables and so on.

many thanks and best regards,

hans

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