Re: Scaling further up - Mailing list pgsql-performance

From Paul Thomas
Subject Re: Scaling further up
Date
Msg-id 20040304005208.A25816@bacon
Whole thread Raw
In response to Re: Scaling further up  ("scott.marlowe" <scott.marlowe@ihs.com>)
Responses Re: Scaling further up  ("scott.marlowe" <scott.marlowe@ihs.com>)
List pgsql-performance
On 03/03/2004 18:23 scott.marlowe wrote:
> [snip]
> There are three factors that affect how fast you can get to the next
> sector:
>
> seek time
> settle time
> rotational latency
>
> Most drives only list the first, and don't bother to mention the other
> two.

Ah yes, one of my (very) few still functioning brain cells was nagging
about another bit of time in the equation :)

> On many modern drives, the seek times are around 5 to 10 milliseconds.
> [snip]

Going back to the OPs posting about random_page_cost, imagine I have 2
servers identical in every way except the disk drive. Server A has a 10K
rpm drive and server B has a 15K rpm drive. Seek/settle times aren't
spectacularly different between the 2 drives. I'm wondering if drive B
might actually merit a _higher_ random_page_cost than drive A as, once it
gets settled on a disk track, it can suck the data off a lot faster.
opinions/experiences anyone?


--
Paul Thomas
+------------------------------+---------------------------------------------+
| Thomas Micro Systems Limited | Software Solutions for the Smaller
Business |
| Computer Consultants         |
http://www.thomas-micro-systems-ltd.co.uk   |
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