[PATCH 8/8] vinyl: keep track of thread pool idle ratio

[Vladimir Davydov]

On Thu, Sep 06, 2018 at 10:49:37AM +0300, Konstantin Osipov wrote:
> * Vladimir Davydov <vdavydov.dev at gmail.com> [18/09/04 20:59]:
> > To understand whether the disk is fully utilized or can still handle
> > more compaction load and make right decisions regarding transaction
> > throttling, we need a metric that would report how much time worker
> > threads spent being idle. So this patch adds two new metrics to global
> > statistics, disk.dump_idle_ratio and compact_idle_ratio, which show how
> > much time dump threads and compaction threads were idle, respectively.
> > The metrics are updated using the following formula:
> > 
> >                        idle_time
> >   idle_ratio = --------------------------
> >                dump_period * worker_count
> 
> I don't understand the formula. There can be many workers.
> Is idle time measured per worker or per entire pool? 
> 
> If it is measured per entire pool, how is idle time calculated if
> some workers are busy and some not?

It is measured for entire pool - note that I divide the result by
worker_count. E.g. if there were two workers and one of them were
busy all the time between two last dumps while another were idle,
idle_ratio would be 0.5.