| From: | David Lang <david(at)lang(dot)hm> |
|---|---|
| To: | Joost Kraaijeveld <J(dot)Kraaijeveld(at)Askesis(dot)nl> |
| Cc: | Richard Huxton <dev(at)archonet(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: x206-x225 |
| Date: | 2006-03-11 07:57:16 |
| Message-ID: | Pine.LNX.4.62.0603102355550.23148@qnivq.ynat.uz |
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| Lists: | 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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