[tarantool-patches] Re: [PATCH v2 1/2] swim: disseminate event for log(cluster_size) steps

[Konstantin Osipov]

* Vladislav Shpilevoy <v.shpilevoy at tarantool.org> [19/07/04 10:15]:
> >> +	/*
> >> +	 * Logarithm is a perfect number of disseminations of an
> >> +	 * event.
> >> +	 *
> >> +	 * Firstly, it matches the dissemination speed.
> >> +	 *
> >> +	 * Secondly, bigger number of disseminations (for example,
> >> +	 * linear) causes events and anti-entropy starvation in
> >> +	 * big clusters, when lots of events occupy the whole UDP
> >> +	 * packet, and factually the same packet content is being
> >> +	 * sent for quite a long time. No randomness. Anti-entropy
> >> +	 * does not get a chance to disseminate something new and
> >> +	 * random. Bigger orders are redundant and harmful.
> >> +	 *
> >> +	 * Thirdly, logarithm is proved by the original
> >> +	 * SWIM paper as the best option.
> >> +	 */
> >> +	member->status_ttd = ceil(log2(mh_size(swim->members)));
> 
> I've changed this place to
> 
>     member->status_ttd = ceil(log2(mh_size(swim->members))) + 1;
> 
> It allows to do not break the tests in this commit, and fixes a bug,
> when status_ttd became negative for 'self'. Because ceil(log2(1)) = 0,
> and on a next round step it became -1, -2, etc.
> 
> I didn't push the patch yet, if you have anything against that.

go ahead and push

-- 
Konstantin Osipov, Moscow, Russia