I have seen something similar and agree it that MySQL is the likely culprit. Turning on the slow query log in MySQL may show you some of the queries that are taking long but once they start stacking up then everything winds up slow and going into the log. Make sure to run the explain plan on all your queries and analyze them carefully. A few months back we restarted a mysql instance without changing anything and I/O went through the roof. Running explain looked ok but when our DBA grouped up with the app developer they figured out the mysql wasn't taking the best path to retrieving the data. They modified the query and load went back to normal.
- Anthony Lopez -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Trevor Hemsley Sent: Monday, July 20, 2009 3:26 PM To: Red Hat Enterprise Linux 5 (Tikanga) discussion mailing-list Subject: Re: [rhelv5-list] High I/O Wait on RHEL 5 Server Running MySQL My first point of call on a problem like this would be to ask what MySQL queries were running at the time. Stephen John Smoogen wrote: > On Mon, Jul 20, 2009 at 10:33 AM, Mohd Irwan Jamaluddin<[email protected]> wrote: > >> On Tue, Jul 21, 2009 at 12:25 AM, Eugene Vilensky <[email protected]> wrote: >> >>>> 1) Do I have any justification to relate the slowness of MySQL database and >>>> high I/O Wait? >>>> 2) How I could trace the root cause of high I/O Wait? >>>> 3) What are the impact of high I/O Wait to the system? >>>> >>> You have disks that are either slow or acting slow. What kind of >>> storage are you using for this application? >>> >>> >> This server is connected to HP Modular Smart Array, a Direct Attached Storage. >> >> > > > Going to need more info than that: > 1) What kind of disks (type, speed, size, iops) > 2) How many disks > 3) How are they 'raided' > 4) What type of controller is being used > > > -- Trevor Hemsley Infrastructure Engineer ................................................. * C A L Y P S O * 4th Floor, Tower Point, 44 North Road, Brighton, BN1 1YR, UK OFFICE +44 (0) 1273 666 350 FAX +44 (0) 1273 666 351 ................................................. www.calypso.com This electronic-mail might contain confidential information intended only for the use by the entity named. If the reader of this message is not the intended recipient, the reader is hereby notified that any dissemination, distribution or copying is strictly prohibited. * P * /*/ Please consider the environment before printing this e-mail /*/ _______________________________________________ rhelv5-list mailing list [email protected] https://www.redhat.com/mailman/listinfo/rhelv5-list _______________________________________________ rhelv5-list mailing list [email protected] https://www.redhat.com/mailman/listinfo/rhelv5-list
