Performance Issues When Using Concurrent Dictionary in C# with High Volume Writes
I'm currently working on a C# application that utilizes `ConcurrentDictionary<TKey, TValue>` for managing a cache of user sessions. However, I've noticed significant performance degradation when multiple threads attempt to write to the dictionary simultaneously. Despite using the `AddOrUpdate` method, I've encountered frequent delays and timeouts that seem to correlate with increased write operations. Here's a simplified version of the code I'm implementing: ```csharp ConcurrentDictionary<string, UserSession> sessions = new ConcurrentDictionary<string, UserSession>(); public void UpdateUserSession(string userId, UserSession session) { sessions.AddOrUpdate(userId, session, (key, oldValue) => session); } public void SimulateConcurrentUpdates() { Parallel.For(0, 1000, i => { var userId = "user" + (i % 100); var session = new UserSession { LastAccessed = DateTime.UtcNow }; UpdateUserSession(userId, session); }); } ``` I've tried to ensure that the dictionary operations are as efficient as possible, but the performance issues persist, particularly when `SimulateConcurrentUpdates` executes with high concurrency. The method takes significantly longer than expected, sometimes leading to a timeout when accessing the sessions. I've also monitored the CPU and memory usage, and they seem fine, but the application does become unresponsive during peak write times. Is there any optimization I can implement, or am I approaching the design pattern incorrectly? Also, are there any known issues with `ConcurrentDictionary` in high-write scenarios that I should be aware of? Any guidance or suggestions would be greatly appreciated!