slow API response times in .NET Core

Question

How can I troubleshoot slow API response times in .NET Core?

Vishal Yelve · Answer

1. Measure and Profile Tools: Application Insights (Azure) dotTrace / dotMemory / dotCover (JetBrains) Visual Studio Diagnostic Tools MiniProfiler PerfView (for deeper inspection) Look for: Long request durations Slow database calls High CPU/memory usage Thread pool exhaustion GC (Garbage Collection) pressure 2. Enable Logging Make sure you’re using structured logging with one of the providers: builder.Logging.AddConsole(); builder.Logging.AddDebug(); Or use Serilog , NLog , or Seq for richer diagnostics. Check logs for: Exceptions or timeouts Retries Middleware bottlenecks 3. Check Middleware Pipeline Slow APIs might result from inefficient middleware execution. Example: app.UseMiddleware (); app.UseRouting(); app.UseAuthorization(); // Place order properly Tips: Minimize synchronous I/O Ensure await is used properly (avoid Task.Result or Wait() ) 4. Inspect Database Calls If you're using EF Core or Dapper: Enable SQL logging Use ToListAsync() instead of ToList().Result Avoid N+1 queries Profile using SQL Server Profiler or EF Core logging EF Core Example: var users = await _dbContext.Users .AsNoTracking() .Where(u => u.IsActive) .ToListAsync(); 5. Threading and Asynchronous Code Poor async/await usage can lead to thread pool starvation or deadlocks. Check: Are you using ConfigureAwait(false) where appropriate? Are there blocking calls like .Result , .Wait() ? 6. External API or I/O Calls If your API calls other services: Add timeouts using HttpClient.Timeout Use Polly for retries and circuit breakers Log time taken by external calls Example with Polly: Policy .Handle () .WaitAndRetryAsync(3, retryAttempt => TimeSpan.FromSeconds(retryAttempt)); 7. Caching Lack of caching (or inefficient caching) can slow down responses. Use: In-memory caching ( IMemoryCache ) Distributed cache (Redis) Output caching (.NET 7+) 8. Benchmark Specific Endpoints Use tools like: Postman Apache Benchmark ( ab ) wrk BenchmarkDotNet (for microbenchmarking) 9. Infrastructure Checks Is the API hosted in a properly sized environment (CPU, memory)? Are containers throttling resources? Any latency in cloud services (Azure, AWS)? Check Kestrel and IIS (or nginx) tuning: MaxConcurrentConnections RequestTimeouts App Pool settings 10. Final Tip: Use APM (Application Performance Monitoring) Use tools like: New Relic Dynatrace Datadog Azure Application Insights They can point out: Hot paths Slowest methods Dependency latencies

slow API response times in .NET Core

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