Re: [PATCH 5/8] vinyl: use separate thread pools for dump and compaction tasks

[Konstantin Osipov <kostja@tarantool.org>]

* Vladimir Davydov <vdavydov.dev@gmail.com> [18/09/04 20:59]:
> Using the same thread pool for both dump and compaction tasks makes
> estimation of dump bandwidth unstable. For instance, if we have four
> worker threads, then the observed dump bandwidth may vary from X if
> there's high compaction demand and all worker threads tend to be busy
> with compaction tasks to 4 * X if there's no compaction demand. As a
> result, we can overestimate the dump bandwidth and trigger dump when
> it's too late, which will result in hitting the limit before dump is
> complete and hence stalling write transactions, which is unacceptable.
> 
> To avoid that, let's separate thread pools used for dump and compaction
> tasks. Since LSM tree based design typically implies high levels of
> write amplification, let's allocate 1/4th of all threads for dump tasks
> and use the rest exclusively for compaction.

Please follow this up by changing the default number of write
threads to 4 and making 4 the lower bound for this configuration
setting.

Thanks.
> --
-- 
Konstantin Osipov, Moscow, Russia, +7 903 626 22 32
http://tarantool.io - www.twitter.com/kostja_osipov