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

Darshan Adakane · Answer

Vishal has given excellent steps to your answer. If you wish to troubleshoot slow .NET Core API responses in quicckly, follow these steps: Trace the Path: Use Application Insights or OpenTelemetry to determine if the delay is in the Database , External API calls , or Your Code . Check for Blocking Calls: Search for .Result or .Wait() . Replace them with await to prevent Thread Pool Starvation , which is the leading cause of API hanging under load. Optimize Database (EF Core): Add .AsNoTracking() to read-only queries to save memory. Ensure you are using Pagination ( .Skip() / .Take() ) rather than returning full tables. Verify that frequently filtered columns have Indexes in your database. Audit JSON Payloads: Large JSON objects slow down serialization. Use Response Compression and only return necessary fields via DTOs. Implement Caching: Use IMemoryCache for static data or Redis for distributed environments to avoid redundant processing. I would just ask you to start with quick check on step 3 because that is where most of times API calls slowness might occur, and then move to step 1 if step 1 doesn't work to find the root cause. Hope this helps.

slow API response times in .NET Core

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