Query Redis memory usage per key using C#

query_redis_key_memory_usage.cs

using System;
using System.Net.Http;
using System.Threading.Tasks;
using Newtonsoft.Json.Linq;
using StackExchange.Redis;

namespace query_redis_memory_usage
{
    class Program
    {
        static async Task Main(string[] args)
        {
            var connectionString = "127.0.0.1:6379";
            var connectionConfiguration = ConfigurationOptions.Parse(connectionString);
            var connection = await ConnectionMultiplexer.ConnectAsync(connectionConfiguration).ConfigureAwait(false);

            var database = connection.GetDatabase(0);
            var cursor = "0"; 
            var keyMemoryMap = new Dictionary<string, long>();

            do
            {
                var result = (RedisResult[])await database.ExecuteAsync("SCAN", cursor, "COUNT", 500);
                cursor = (string)result[0];

                var keys = (RedisResult[])result[1];
                var batch = database.CreateBatch();
                var tasks = new List<(string, Task<RedisResult>)>();
                foreach (var key in keys)
                {
                    var keyName = (string)key;
                    var memoryOperation = batch.ScriptEvaluateAsync("return redis.call('MEMORY', 'USAGE', KEYS[1])", new RedisKey[] { keyName });
                    tasks.Add((keyName, memoryOperation));
                }
                batch.Execute();
                await Task.WhenAll(tasks.Select(t => t.Item2)).ConfigureAwait(false);

                foreach (var task in tasks)
                {
                    keyMemoryMap[task.Item1] = (long)task.Item2.Result;
                }
            } while (cursor != "0");

            var sortedKeys = keyMemoryMap.OrderByDescending(kv => kv.Value);
            var jsonResult = JToken.FromObject(sortedKeys).ToString();
            await File.WriteAllTextAsync(@"C:\temp\allkeys.json", jsonResult);

            var aggregatedKeys = new Dictionary<string, long>();
            foreach (var (key, value) in keyMemoryMap)
            {
                var masterKey = key.Split(":").First();
                if (aggregatedKeys.TryGetValue(masterKey, out var result))
                {
                    aggregatedKeys[masterKey] = result + value;
                }
                else
                {
                    aggregatedKeys[masterKey] = value;
                }
            }

            var jsonResultAggregated = JToken.FromObject(aggregatedKeys.OrderByDescending(kv => kv.Value)).ToString();
            await File.WriteAllTextAsync(@"C:\temp\allkeysaggregated.json", jsonResultAggregated);

            await connection.CloseAsync();
        }
    }
}

Ran against 1.8 million keys in production (m6g.large instance) without any significant impact on Redis server performance.