[svlug] Sync command slowdown

[Sargun Dhillon]

Why not mount the partition -o sync entirely? ;-P
Also, you should be using the write-back cache on your controller, so
sync should just be a "soft" sync. See if you can turn on the right
back cache on your controller.

On Mon, Nov 24, 2008 at 6:08 PM, Greg Lindahl <lindahl at pbm.com> wrote:
> On Mon, Nov 24, 2008 at 05:32:40PM -0800, James Sparenberg wrote:
>
>>     I've got 4 new DB servers exhibiting a rather problematic set of
>> actions with disk sync.  Running the sync command (as is done when logs
>> are rotated.)  takes 4-6 seconds (not micro, full seconds)  Other than
>> this these boxes are running 10x faster than the servers they replaced
>> and making our customers much happier.
>
> I'd bet that you're ending up with many more dirty pages on the new
> servers because they have more memory than the old ones. You can watch
> this value over time with
>
> % grep Dirty /proc/meminfo
>
> sync is a big club: it syncs all the files in the system instead of
> just the ones you care about. And it can kill performance for other
> processes if there are a lot of pages to be written out.
>
> Doctor, it hurts when I do this.
>
> -- greg
>
>
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