Re: x206-x225 - Mailing list pgsql-performance

From David Lang
Subject Re: x206-x225
Date
Msg-id Pine.LNX.4.62.0603102355550.23148@qnivq.ynat.uz
Whole thread Raw
In response to Re: x206-x225  (Joost Kraaijeveld <J.Kraaijeveld@Askesis.nl>)
Responses Re: x206-x225  (Joost Kraaijeveld <J.Kraaijeveld@Askesis.nl>)
Re: x206-x225  ("Jim C. Nasby" <jnasby@pervasive.com>)
List pgsql-performance
On Sat, 11 Mar 2006, Joost Kraaijeveld wrote:

> On Fri, 2006-03-10 at 13:40 +0000, Richard Huxton wrote:
>> Your ATA disk is lying about disk caching being turned off. Assuming
>> each insert is in a separate transaction, then it's not going to do
>> 10,000 / 6 = 1667 transactions/sec - that's faster than it's rotational
>> speed.
> Could you explain the calculation? Why should the number of transactions
> be related to the rotational speed of the disk, without saying anything
> about the number of bytes per rotation?

each transaction requires a sync to the disk, a sync requires a real
write (which you then wait for), so you can only do one transaction per
rotation.

David Lang

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