Re: default filestore max sync interval

[Stefan Priebe <s.priebe@profihost.ag>]

H Greg,


Am 29.04.2014 22:23, schrieb Gregory Farnum:
> On Tue, Apr 29, 2014 at 1:10 PM, Dan Van Der Ster
> <daniel.vanderster@cern.ch> wrote:
>> Hi all,
>> Why is the default max sync interval only 5 seconds?
>>
>> Today we realized what a huge difference that increasing this to 30 or 60s can do for the small write latency. Basically, with a 5s interval our 4k write latency is above 30-35ms and once we increase it to 30s we can get under 10ms (using spinning disks for journal and data.)
>>
>> See the attached plot for the affect of this on a running cluster (the plot shows the max, avg, min write latency from a short rados bench every 10 mins). The change from 5s to 60s was applied at noon today. (And our journals are large enough, don't worry).
>>
>> In the interest of having sensible defaults, is there any reason not to increase this to 30s?
>
> If you've got reasonable confidence in the quality of your
> measurements across the workloads you serve, you should bump it up.
> Part of what might be happening here is simply that fewer of your
> small-io writes are running into a sync interval.
> I suspect that most users will see improvement by bumping up the
> limits and occasionally agitate to change the defaults, but Sam has
> always pushed back against doing so for reasons I don't entirely
> recall. :) (The potential for a burstier throughput profile?)
> -Greg

What is about those?

         filestore queue max ops = 500
         filestore_queue_committing_max_ops = 5000
         filestore_queue_max_bytes = 419430400
         filestore_queue_committing_max_bytes = 419430400

   filestore_wbthrottle_xfs_bytes_start_flusher = 125829120
   filestore_wbthrottle_xfs_bytes_hard_limit = 419430400
   filestore_wbthrottle_xfs_ios_start_flusher = 5000
   filestore_wbthrottle_xfs_ios_hard_limit = 50000
   filestore_wbthrottle_xfs_inodes_start_flusher = 1000
   filestore_wbthrottle_xfs_inodes_hard_limit = 10000

They should be adjusted too? right?

Stefan