RedisReadTopCategories.cs

public IEnumerable<Category> ReadTopCategories(int offset, int countCategories)
{
    var cache = _muxer.GetDatabase();
    var res = cache.SortedSetRangeByRankWithScores("CategoriesByPostCount", offset, offset + countCategories -1, Order.Descending);
    var ret = new List<Category>();
    foreach(var e in res)
    {
        ret.Add(new Category { CategoryId = e.Element, PostCount = (long)e.Score });
    }
    return ret;
}