Re: WIP: Fast GiST index build

On 25.06.2011 11:23, Alexander Korotkov wrote:
> On Sat, Jun 25, 2011 at 11:03 AM, Jesper Krogh<jesper(at)krogh(dot)cc> wrote:
>
>> * Wouldn't it be natural to measure the performance benefits of
>> disc-bound tests in an SSD setup?
>>
> Sure, it would be great to run performance tests on SSD drives too.
> Unfortunately, I don't have corresponding test platform just now.

Anyone have an SSD setup to run some quick tests with this?

>> In terms of random IO an SSD can easily be x100 better than rotating
>> drives and it would be a shame to optimize "against" that world?
>
> Actually, I'm not sure that IO is bottle neck of GiST index build on SSD
> drives. It's more likely for me that CPU becomes a bottle neck in this case
> and optimizing IO can't give much benefit. But anyway, the value of this
> work can be in producing better index in some cases and SSD drive lifetime
> economy due to less IO operations.

Yeah, this patch probably doesn't give much benefit on SSDs, not the
order of magnitude improvements it gives on HDDs anyway. I would expect
there to still be a small gain, however. If you look at the comparison
of CPU times on Alexander's tests, the patch doesn't add that much CPU
overhead: about 5% on the point_ops tests. I/O isn't free on SSDs
either, so I would expect the patch to buy back that 5% increase in CPU
overhead by reduced time spent on I/O even on a SSD.

It's much worse on the gist_trgm_ops test case, so this clearly depends
a lot on the opclass, but even that should be possible to optimize quite
a bit.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com