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Re: WIP: Fast GiST index build

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Alexander Korotkov <aekorotkov(at)gmail(dot)com>
Cc: Jesper Krogh <jesper(at)krogh(dot)cc>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: WIP: Fast GiST index build
Date: 2011-06-26 10:18:06
Message-ID: 4E07075E.30900@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-hackers
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

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