The case when we choose bad hash function resulting in flip of the traffic

partitions-flip-traffix.cs

// See https://aka.ms/new-console-template for more information
Console.WriteLine("Hello, World!");


var dict = new Dictionary<string, int>
{
    ["euwe-0"] = 0,
    ["euno-0"] = 0,
    ["euwe-1"] = 0,
    ["euno-1"] = 0,
    ["euwe-2"] = 0,
    ["euno-2"] = 0,
    ["euwe-3"] = 0,
    ["euno-3"] = 0,
};

// we have 2 regions: euwe and euno
// we have 4 partitions: 00, 01, 02, 03

for (var i = 0; i < 100000; i++)
{
    var partitionKey = $"somestatic{i}somestatic2";
    var regionKey = $"{i}";

    var partitionId = Math.Abs(GetHashCode(partitionKey)) % 4;
    var regionId = Math.Abs(GetHashCode(regionKey)) % 2;

    var reg = regionId == 0 ? "euwe" : "euno";
    var dictKey = $"{reg}-{partitionId}";

    if (!dict.ContainsKey(dictKey))
    {
        dict.Add(dictKey, 0);
    }

    dict[dictKey]++;
}

Console.WriteLine(dict.Count);

static int GetHashCode(string input)
{
    return input.GetHashCode();

    //uint hash = 0;
    //for (int inputCharIndex = 0; inputCharIndex < input.Length; ++inputCharIndex)
    //{
    //    uint inputCharValue = input[inputCharIndex];
    //    hash = inputCharValue + (hash << 6) + (hash << 16) - hash;
    //}

    //int result = (int)hash;

    //return result;
}