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From dsetrak...@apache.org
Subject Re: Resurrect FairAffinityFunction
Date Tue, 25 Jul 2017 02:13:18 GMT
Agree with Val, we should bring it back.


On Jul 24, 2017, 8:14 PM, at 8:14 PM, Valentin Kulichenko <valentin.kulichenko@gmail.com>
>Some time ago we removed FairAffinityFunction from the project.
>However, my
>communication with users clearly shows that is was a rush decision.
>Distribution showed by Fair AF is much better than default and for some
>users it's extremely important. Basically, there are cases when
>function is no-go.
>The reason for removal was that it was possible to get inconsistent
>in case multiple caches were created on different topologies. However,
>think this is fixable. As far as I understand, the only thing we need
>to do
>is to maintain a single AffinityFunctionContext for all the caches with
>same affinity function. Currently for each cache we have separate
>which holds the state used by Fair AF. If the state is different, we
>an issue.
>The only question is how to check whether two functions are the same or
>not. In case both cache node filter and backup filter are not
>this is easy - if number of partitions and excludeNeighbors flag are
>for two functions, these functions are also equal.
>With filters it's a bit more complicated as these are custom
>implementations and in general case we don't know how to compare them.
>Although, to solve this problem, we can enforce user to implement
>method for these implementation if Fair AF is used.
>I propose to make changes described above and bring Fair AF back.

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