We have seen the exact same thing here. We used the deadline scheduler
and saw an immediate improvement. However, we still saw much worse
performance on our Opteron's (compared to our older Xeon boxes). We
ended up rolling back to Fedora Core 1 2.4.22-1.2199.nptlsmp kernel and
shut down NPTL and now our Opteron's are much much faster than our Xeons.
The thing I find strange about this is that our experience (@ Meetup)
seems to match that of Friendsters (I know of a few other high traffic
sites that have mentioned similar issues), in that Mysql on Opteron and
Linux 2.6 is not a good solution. Yet, Mysql recommends exactly this
config and in fact, does not seem to even support (via support contract)
a 2.4 solution for Opteron + Mysql.
Greg
Dathan Pattishall wrote:
> What kernel are you running.
>
> If your running 2.6.x use the deadline scheduler or downgrade to
> 2.4.23aavm 2.6.[0-9] has major problems with the IO scheduler since the
> process scheduler is very fast now.
>
>
> DVP
> ----
> Dathan Vance Pattishall http://www.friendster.com
>
>
>
>
>>-----Original Message-----
>>From: Kevin Burton [mailto:burton@stripped]
>>Sent: Friday, May 06, 2005 1:58 PM
>>To: mysql@stripped
>>Subject: MySQL not using optimum disk throughput.
>>
>>
>>We have a few of DBs which aren't using disk IO to optimum capacity.
>>
>>They're running at a load of 1.5 or so with a high workload
>>of pending queries.
>>
>>When I do iostat I'm not noticing much IO :
>>
>>Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s
>> wkB/s
>>avgrq-sz avgqu-sz await svctm %util
>>sda 0.00 13.73 128.43 252.94 1027.45 1695.10 513.73
>>847.55 7.14 90.13 285.00 2.53 96.57
>>
>>....
>>
>>This is only seeing about 500k -> 1M per second throughput.
>>
>>When I run bonnie++ on these drives they're showing 20M->40M
>>throughput.
>>
>>Which is really strange.
>>
>>Most of our queries are single INSERTS/DELETES. I could
>>probably rewrite these to become batch operations but I think
>>I'd still end up seeing the above iostat results but with
>>higher throughput.
>>
>>.... so I'd like to get to the bottom of this before moving forward?
>>
>>I ran OPTIMIZE TABLE on all tables but nothing.
>>
>>The boxes aren't paging.
>>
>>They're running on a RAID5 disk on XFS.
>>
>>Could it be that the disks are having to do a number of HEAD
>>seeks since we have large tables?
>>
>>--
>>
>>
>>Use Rojo (RSS/Atom aggregator)! - visit http://rojo.com.
>>See irc.freenode.net #rojo if you want to chat.
>>
>>Rojo is Hiring! - http://www.rojonetworks.com/JobsAtRojo.html
>>
>> Kevin A. Burton, Location - San Francisco, CA
>> AIM/YIM - sfburtonator, Web - http://peerfear.org/ GPG
>>fingerprint: 5FB2 F3E2 760E 70A8 6174 D393 E84D 8D04 99F1 4412
>>
>>
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>>
>>
>
>
