[CentOS] IO causing major performance issues

Ross S. W. Walker rwalker at medallion.com
Thu Nov 15 23:02:43 UTC 2007

Les Mikesell wrote:
> Ross S. W. Walker wrote:
> > 
> > Yes, IO starvation can occur under heavy load.
> But it should stall the process needing to write, not everything.

There is only 1 disk though and if that disk is busy writing it
can't read.

It would be nice if disk manufacturers made full duplex disks
with 1 set of heads for writing and another set of heads for
reading, but they don't :-( 

> > Don't put database temp tables on system disks (or data 
> tables for that matter).
> > 
> > How much memory do you have in this box and how big does 
> the temp directory
> > usage get?
> > 
> > Why I ask is you could create a tempfs and have mysql use 
> that, just make sure
> > you have enough memory that you can spare X (whatever your 
> temp table usage is)
> > for a cache filesystem.
> > 
> > You would also notice a dramatic speed increase in MySQL.
> I'm not sure the needed temp table space is predictable.  I've seen 
> mysql be pretty dumb about how it does a select that joins 
> several tables.

True, but take an average and that should suffice, MySQL will wait
if temp space fills up.


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