Sequential I/O Cost (was Re: A Better External Sort?)
От | Jeffrey W. Baker |
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Тема | Sequential I/O Cost (was Re: A Better External Sort?) |
Дата | |
Msg-id | 1127968426.8954.19.camel@noodles обсуждение исходный текст |
Ответ на | Re: [HACKERS] A Better External Sort? (Ron Peacetree <rjpeace@earthlink.net>) |
Список | pgsql-performance |
On Wed, 2005-09-28 at 12:03 -0400, Ron Peacetree wrote: > >From: "Jeffrey W. Baker" <jwbaker@acm.org> > >Perhaps I believe this because you can now buy as much sequential I/O > >as you want. Random I/O is the only real savings. > > > 1= No, you can not "buy as much sequential IO as you want". Even if > with an infinite budget, there are physical and engineering limits. Long > before you reach those limits, you will pay exponentially increasing costs > for linearly increasing performance gains. So even if you _can_ buy a > certain level of sequential IO, it may not be the most efficient way to > spend money. This is just false. You can buy sequential I/O for linear money up to and beyond your platform's main memory bandwidth. Even 1GB/sec will severely tax memory bandwidth of mainstream platforms, and you can achieve this rate for a modest cost. I have one array that can supply this rate and it has only 15 disks. It would fit on my desk. I think your dire talk about the limits of science and engineering may be a tad overblown.
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