[GRLUG] FYI - old mysql and new gear

[scott.tanner at comcast.net]

I'm going to try using affinity to limit the CPU access and run a few benchmarks - should be an interesting test. 

I've heard there's a fair amount of overhead when running MySQL in virtual machines, specifically due to the abstraction layer between the raid controller and guest. It would be interesting to test, but difficult to setup now that the server is running in production - It doesn't look like you can limit the number of processors for Dom0. 

We purposely don't run anything else on these servers to reduce any contention, so limiting the CPU's isn't a very big deal, however wasting 4 / 16 cores (real / +HT) is pretty silly. 

Thanks guys! 
Scott 
----- Original Message -----
From: "Ben Rousch" <brousch at gmail.com> 
To: "Mailing List for LUG in greater Grand Rapids, MI area." <grlug at grlug.org> 
Sent: Monday, September 19, 2011 4:56:22 PM 
Subject: Re: [GRLUG] FYI - old mysql and new gear 

On Mon, Sep 19, 2011 at 4:45 PM, Michael Mol <mikemol at gmail.com> wrote: 
> On Mon, Sep 19, 2011 at 4:36 PM, <scott.tanner at comcast.net> wrote: 
>> Just thought I'd share an interesting discovery with the group. This may be 
>> common knowledge to others, but it was a bit of a surprise to me. We're in 
>> the process of upgrading the servers which run our primary MySQL DB's 
>> (version 5.1): 
>> 
>> Old Server New Server 
>> --------------------------------------------------------- 
>> Sun X4200 Silicon Mechanics R516 
>> 4 x 2.4GHz 12 x 3.2GHz (+ HT = 24 threads) 
>> 16GB Ram 144GB Ram 
>> 12 disks - SCSI 24 disks - SAS & SSD 
>> 
>> 
>> After getting the new servers setup and our databases copied over, I ran 
>> sysbench to get some performance benchmarks of the new servers. Surprise - 
>> performance was nearly identical or slightly worse. I disabled HT, still no 
>> real improvement. After a bit of searching on the web, I found the older 
>> versions of MySQL had issues with multi-threading beyond 8 threads. I setup 
>> an init script to hot-remove CPU's via sysfs, and voila - performance 
>> increased substantially. There are patches from Yahoo, Google, and Percona 
>> to correct this issue on the older MySQL versions, and the newer versions 
>> are supposedly better at handling 32+ threads. 
> 
> Very interesting. 
> 
> A thought...Rather than removing your extra cores, perhaps there's 
> some way to set CPU affinity, so MySQL is only allowed to use eight of 
> them? That way, the other processes on your system can stay out of the 
> way of your database server, and spend cycles on other cores. 
> 
> If you get affinities working, you might also consider running 
> multiple instances of mysqld, putting different databases on different 
> sets of cores. 

How about putting it in a virtual machine that only has access to 8 cores? 

-- 
Ben Rousch 
brousch at gmail.com 
http://clusterbleep.net/ 

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