Open Stack

Maybe we should change how we wait?

I get that we don't want to sit around forever, but perhaps we should
specify a total maximum time to wait instead of a number of iterations
of a loop? Something like "15 minutes should be long enough for
anyone!". Eventlet sleeps are also pretty cheap, so having a bigger
sleep time inside them just means that we overshoot more than we would
otherwise.

Michael

On Thu, Aug 7, 2014 at 3:54 AM, Jay Pipes <jaypipes at gmail.com> wrote:
> Hi Stackers!
>
> So, Liyi Meng has an interesting patch up for Nova:
>
> https://review.openstack.org/#/c/104876
>
> that changes the way that the interval and number of retries is calculated
> for a piece of code that waits around for a block device mapping to become
> active.
>
> Namely, the patch discards the value of the following configuration options
> *if the volume size is not 0* (which is a typical case):
>
> * CONF.block_device_allocate_retries_interval
> * CONF.block_device_allocate_retries
>
> and in their place, instead uses a hard-coded 60 max number of retries and
> calculates a more "appropriate" interval by looking at the size of the
> volume to be created. The algorithm uses the sensible idea that it will take
> longer to allocate larger volumes than smaller volumes, and therefore the
> interval time for larger volumes should be longer than smaller ones.
>
> So... here's the question: since this code essentially makes the above two
> configuration options obselete for the majority of cases (where volume size
> is not 0), should we do one of the following?
>
> 1) We should just deprecate both the options, with a note in the option help
> text that these options are not used when volume size is not 0, and that the
> interval is calculated based on volume size
>
> or
>
> 2) We should deprecate the CONF.block_device_allocate_retries_interval
> option only, and keep the CONF.block_device_allocate_retries configuration
> option as-is, changing the help text to read something like "Max number of
> retries. We calculate the interval of the retry based on the size of the
> volume."
>
> I bring this up on the mailing list because I think Liyi's patch offers an
> interesting future direction to the way that we think about our retry
> approach in Nova. Instead of having hard-coded or configurable interval
> times, I think Liyi's approach of calculating the interval length based on
> some input values is a good direction to take.
>
> Thoughts?
>
> -jay
>
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