[Gluster-devel] Throttling xlator on the bricks

[Shreyas Siravara]

So the way our throttling works is (intentionally) very simplistic. 

(1) When someone mounts an NFS share, we tag the frame with a 32 bit hash of the export name they were authorized to mount.
(2) io-stats keeps track of the "current rate" of fops we're seeing for that particular mount, using a sampling of fops and a moving average over a short period of time.
(3) Based on whether the share violated its allowed rate (which is defined in a config file), we tag the FOP as "least-pri". Of course this makes the assumption that all NFS endpoints are receiving roughly the same # of FOPs. The rate defined in the config file is a *per* NFS endpoint number. So if your cluster has 10 NFS endpoints, and you've pre-computed that it can do roughly 1000 FOPs per second, the rate in the config file would be 100.
(4) IO-Threads then shoves the FOP into the least-pri queue, rather than its default. The value is honored all the way down to the bricks.

The code is actually complete, and I'll put it up for review after we iron out a few minor issues.

> On Jan 27, 2016, at 9:48 PM, Ravishankar N <ravishankar at redhat.com> wrote:
> 
> On 01/26/2016 08:41 AM, Richard Wareing wrote:
>> In any event, it might be worth having Shreyas detail his throttling feature (that can throttle any directory hierarchy no less) to illustrate how a simpler design can achieve similar results to these more complicated (and it follows....bug prone) approaches.
>> 
>> Richard
> Hi Shreyas,
> 
> Wondering if you can share the details of the throttling feature you're working on. Even if there's no code, a description of what it is trying to achieve and how will be great.
> 
> Thanks,
> Ravi