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From: Matthew Nuzum (matt.followers_at_gmail.com)
Date: Thu 31 Mar 2005 - 18:09:24 BST

> >
> > would it be possilble to limit write/read speed for single vservers
> to
> > split
> >
> > the speed of the disc? For vservers with many copy,gzip or in
> special
> > backup jobs it would be quite usefull.
> hmm, so you would like to artificially slow down the
> I/O transfer of a vserver, and make the transaction
> somewhat longer than necessary?
> best,
> Herbert

Actually, it's very easy for a long running PostgreSQL query to consume all
of the i/o bandwidth on a server. I've had this happen where a seq scan on a
database with many millions of records on an IDE disk has effectively hosed
the server for an hour or more.

Of course, I am the administrator for all of my virtual servers so I plan
around these types of batch jobs, but if I were setting up a hosting
environment and gave vserver root access to others I'd be concerned.

This would be very easy to duplicate by creating a db table with 20 million
random values and then doing a query like this: select min(rand_val) as min,
max(rand_val) as max from table1; Just make sure there are no indexes on the
table of course. Also make sure the size of the database table is bigger
than the amount of RAM the OS can use for caching.

Matthew Nuzum <matt_at_followers.net>
www.followers.net - Makers of "Elite Content Management System"
View samples of Elite CMS in action by visiting

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