diff --git a/src/WeihanLi.Common/Helpers/InMemoryStream.cs b/src/WeihanLi.Common/Helpers/InMemoryStream.cs
index 068ed560..4c265f14 100644
--- a/src/WeihanLi.Common/Helpers/InMemoryStream.cs
+++ b/src/WeihanLi.Common/Helpers/InMemoryStream.cs
@@ -1,7 +1,5 @@
-// Copyright (c) Weihan Li. All rights reserved.
-// Licensed under the Apache license.
-
 using System.Collections.Concurrent;
+using System.Runtime.CompilerServices;
 using WeihanLi.Common.Models;
 using WeihanLi.Extensions;
 
@@ -49,8 +47,9 @@ public interface IStream<T>
 
 public sealed class InMemoryStream<T>(string name, IComparer<T>? comparer = null) : IStream<T>
 {
-    private readonly PriorityQueue<StreamMessage<T>, T> _messages = new(comparer);
+    private readonly List<StreamMessage<T>> _messages = new();
     private readonly ConcurrentDictionary<string, StreamGroupInfo<T>> _groups = new();
+    private readonly IComparer<T> _comparer = comparer ?? Comparer<T>.Default;
 
     public string StreamName => name;
 
@@ -74,7 +73,7 @@ public Task AddAsync(T id, Dictionary<string, string> fields, DateTimeOffset? ti
             Timestamp = timestamp ?? DateTimeOffset.Now,
             Properties = properties ?? new()
         };
-        _messages.Enqueue(message, id);
+        _messages.Add(message);
 
         return Task.CompletedTask;
     }
@@ -83,7 +82,7 @@ public Task AddGroupAsync(string groupName, T offset, CancellationToken cancella
     {
         if (_groups.ContainsKey(groupName))
         {
-            throw new InvalidOperationException($"Group [{groupName}] not exists");
+            throw new InvalidOperationException($"Group [{groupName}] already exists");
         }
 
         _groups[groupName] = new StreamGroupInfo<T>()
@@ -96,13 +95,43 @@ public Task AddGroupAsync(string groupName, T offset, CancellationToken cancella
 
     public Task<int> CountAsync(T? min = default, T? max = default, RangeInclusion inclusion = default, CancellationToken cancellationToken = default)
     {
-        // TODO: support min/max filter
-        return _messages.Count.WrapTask();
+        var count = _messages.Count;
+        if (min != null || max != null)
+        {
+            count = _messages.Count(item =>
+            {
+                var id = item.Id;
+                var isInRange = true;
+                if (min != null)
+                {
+                    isInRange = inclusion.HasFlag(RangeInclusion.IncludeLowerBound) ? _comparer.Compare(id, min) >= 0 : _comparer.Compare(id, min) > 0;
+                }
+                if (max != null)
+                {
+                    isInRange = inclusion.HasFlag(RangeInclusion.IncludeUpperBound) ? _comparer.Compare(id, max) <= 0 : _comparer.Compare(id, max) < 0;
+                }
+                return isInRange;
+            });
+        }
+        return Task.FromResult(count);
     }
 
-    public IAsyncEnumerable<StreamMessage<T>> FetchAsync(T lastId, int count, Ordering order = Ordering.Ascending, CancellationToken cancellationToken = default)
+    public async IAsyncEnumerable<StreamMessage<T>> FetchAsync(T lastId, int count, Ordering order = Ordering.Ascending, [EnumeratorCancellation] CancellationToken cancellationToken = default)
     {
-        throw new NotImplementedException();
+        var messages = order == Ordering.Ascending ? _messages.OrderBy(item => item.Id) : _messages.OrderByDescending(item => item.Id);
+        var fetchedCount = 0;
+        foreach (var message in messages)
+        {
+            if (fetchedCount >= count)
+            {
+                yield break;
+            }
+            if (_comparer.Compare(message.Id, lastId) > 0)
+            {
+                yield return message;
+                fetchedCount++;
+            }
+        }
     }
 
     public Task<StreamGroupInfo<T>?> GroupInfoAsync(string groupName, CancellationToken cancellationToken = default)
@@ -122,11 +151,14 @@ public Task<IReadOnlyCollection<StreamGroupInfo<T>>> GroupsAsync(CancellationTok
 
     public Task<StreamInfo<T>> InfoAsync(CancellationToken cancellationToken = default)
     {
+        var minMessage = _messages.MinBy(item => item.Id);
+        var maxMessage = _messages.MaxBy(item => item.Id);
         var streamInfo = new StreamInfo<T>
         {
-            // TODO: update min/max from messages
-            MinId = default,
-            MaxId = default,
+            MinId = minMessage?.Id ?? default,
+            MinTimestamp = minMessage?.Timestamp ?? default,
+            MaxId = maxMessage?.Id ?? default,
+            MaxTimestamp = maxMessage?.Timestamp ?? default,
             Count = _messages.Count
         };
         return streamInfo.WrapTask();