ConsistentHash formula

[rogeralsing]

The ConsistentHash routers in Akka uses Murmur hash to ensure even distribution.
Our version simply uses GetHashCode() atm.
Do we need Murmur hash or is the built in .NET hashcode enough to ensure even distribution among routees?

[HCanber]

Haven't looked at the code, but are the hashes ever used between processes or AppDomains? If yes, then we must implement something else.

[Aaronontheweb]

What a coincidence - I'm working on an open-source HyperLogLog implementation (which we'll be using in combination with Akka.NET) and as part of this I've had to implement Murmur3.

I'm still doing some bugfixes with my Murmur3 implementation, but I should have a copy of it available later this week. I have both a 32-bit Murmur3 and 128-bit Murmur3 implementation, but I'm thinking about canning the 128-bit one. For our purposes it's probably overkill.

[rogeralsing]

Related to #11

[Aaronontheweb]

Here's the Murmur3 implementation I want to use, from MarkedUp's new OpenMetrics project:

https://github.com/markedup-mobi/openmetrics/blob/master/src/MarkedUp.HyperLogLog/Hash/Murmur3.cs

It's been performance tested for collisions and hashing speed (clone the project to find out for yourself ;)) and is based off of the canonical C++ implementation and the developer interface (how it gets used by programmers) is based off of Scala's internal Murmur3 implementation.

I'm planning on lumping this and https://github.com/markedup-mobi/openmetrics/blob/master/src/MarkedUp.HyperLogLog/BitArrayHelpers.cs (used mostly for hashing decimal types) into a single file and drop it directly into Akka.NET in the Utils / Tools space.

Any objections?

[rogeralsing]

    /// Finalization mix - force all bits of a hash block to avalanche.
    /// 
    /// I have no idea what that means but it sound awesome.

👯

Go for it

[HCanber]

+1