[CentOS] IO causing major performance issues

[Les Mikesell]

Ross S. W. Walker 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.

But if it weren't for the accumulation of stuff in the raid card queue, 
other processes should get an equal shot fairly quickly.  I think that 
raid card just treats draining the whole queue as one operation.

>>> 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.

What does that mean if it needs more than the available space to 
complete a single operation - like a multi-table join that decides to 
copy the whole tables to temp files?

-- 
   Les Mikesell
    lesmikesell at gmail.com