Many misuse them. 🧠Difference IHostedService = lifecycle hooks BackgroundService = long-running loops ✅ Rule Use BackgroundService for workers.
Author: ErcanOPAK
Middleware Order Can Break Security
Order matters a lot. ❌ Wrong UseEndpoints(); UseAuthentication(); ✅ Correct UseAuthentication(); UseAuthorization(); UseEndpoints();
NOT IN vs NOT EXISTS — One Can Return Wrong Results
WHERE Id NOT IN (SELECT UserId FROM BannedUsers) ❌ Problem If subquery returns NULL, results are wrong. ✅ Always Safer WHERE NOT EXISTS ( SELECT 1 FROM BannedUsers b WHERE b.UserId = u.Id )
SELECT * Breaks Index Usage
This kills performance: SELECT * FROM Orders 🧠Why Forces key lookups Breaks covering indexes ✅ Fix Select only what you need: SELECT Id, Total FROM Orders
Structs Aren’t Always Faster Than Classes
Many devs assume structs = faster. ❌ Reality Large structs copy memory Passed by value by default ✅ Rule of Thumb Small, immutable → struct Complex objects → class
LINQ ToList() — The Performance Trap
This line is expensive: var users = query.ToList(); 🧠Why Executes immediately Loads everything into memory ✅ Better Stream or filter first: var users = query.Where(x => x.IsActive);
async void — The Exception Black Hole
This should almost never exist: async void DoWork() ❌ Why it’s dangerous Exceptions crash the process Cannot be awaited Impossible to test ✅ Correct async Task DoWorkAsync() Only valid use: event handlers.
Visual Studio Debugger Skips Lines — Optimized Build Trap
Debugger lies when optimization is on. ✅ Fix Build Configuration → DebugDisable Optimize Code
WordPress Admin Slow — Heartbeat API Overload
Heartbeat runs every 15s. âś… Fix Reduce frequency or disable on non-edit pages. Result Lower CPU Faster admin
SSD Slow on Windows 11 — TRIM Disabled
Check: fsutil behavior query DisableDeleteNotify 0 = enabled1 = disabled (bad)
Windows 11 Random Freezes — Power Plan Trap
Balanced mode throttles CPUs aggressively. ✅ Fix Power Settings → High Performance
Silent AJAX Failures — Missing Content-Type
Backend never hits controller? âś… Fix headers: { “Content-Type”: “application/json” }
forEach + async — A Hidden Logic Bug
This does not await: array.forEach(async x => await save(x)); âś… Fix for (const x of array) { await save(x); }
loading=”lazy” — Free Performance Win
<img src=”hero.jpg” loading=”lazy”> Why Faster initial load Lower bandwidth Better Core Web Vitals
100vh Breaks Mobile Layouts — Here’s Why
Mobile browsers resize viewport dynamically. âś… Fix height: 100svh; or JS-calculated height.
HttpClient Socket Exhaustion — Still Happening in 2025
This is wrong: new HttpClient(); âś… Correct builder.Services.AddHttpClient(); Why Reuses sockets Prevents random timeouts
Minimal APIs — Why Filters Replace Middleware
Middleware runs for every request. âś… Endpoint Filter app.MapPost(“/orders”, handler) .AddEndpointFilter<AuthFilter>(); Why Faster Scoped Cleaner
Missing WHERE on UPDATE — Disaster Prevention Trick
Human error happens. âś… Safety Pattern BEGIN TRAN UPDATE Users SET IsActive = 0 WHERE LastLogin < ‘2022-01-01’ — sanity check SELECT @@ROWCOUNT ROLLBACK
Parameter Sniffing — The Query That Works… Until It Doesn’t
Same query, different performance. 🧠Root cause SQL caches execution plans based on the first parameter. ✅ Fix Options OPTION (RECOMPILE) or OPTIMIZE FOR UNKNOWN
ValueTask — Faster but Dangerous
ValueTask<int> GetAsync(); âš Hidden traps Cannot await twice Harder debugging âś… Rule Use only when result is usually synchronous.
ConfigureAwait(false) — When It Actually Matters
Using it everywhere is wrong. ✅ Use it when: Library code No UI / request context needed await httpClient.GetAsync(url) .ConfigureAwait(false); ❌ Avoid in: ASP.NET Core (no sync context) UI event handlers
Task.Run() in ASP.NET — The Silent Scalability Killer
This looks harmless: Task.Run(() => DoWork()); ❌ Why it breaks production Bypasses request lifecycle Ignores cancellation Starves thread pool under load ✅ Correct Pattern Use background services: public class Worker : BackgroundService { protected override async Task ExecuteAsync(CancellationToken ct) { while (!ct.IsCancellationRequested) await DoWorkAsync(ct); } }
Visual Studio “IntelliSense Wrong Types” — Stale Solution Cache
Types show incorrectly? Suggestions are wrong? ✅ Fix Close VS and delete: .vs/ bin/ obj/ Reopen solution → fixed.
WordPress REST API Slow — Disable Unused Endpoints
Every REST route loads on init. âś… Fix Disable what you don’t use via plugin or code: remove_action(‘rest_api_init’, ‘wp_oembed_register_route’); Result Lower memory usage and faster responses.
Windows 11 Laptop Fans Always Loud — Background Indexing
Search indexing runs aggressively on SSDs. ✅ Fix Settings → Privacy → Searching Windows → Reduce indexing scope.
Windows 11 Slow Boot After Updates — Startup App Priority
Windows sometimes re-enables heavy startup apps. ✅ Fix Task Manager → Startup → Disable non-essential apps. Result Faster boot and login.
AJAX Requests Timeout Randomly — Browser Connection Limits
Browsers limit concurrent connections per domain. âś… Fix Throttle requests or queue them: await Promise.allSettled(queue.map(run)); Especially important for dashboards batch uploads
JS “Undefined Is Not Null” — The Bug That Breaks APIs
undefined !== null âś… Defensive Check if (value == null) { // catches both null and undefined } Use strict checks only when you really need them.
HTML5 autocomplete — Stop Browsers From Guessing Wrong
Browsers often autofill incorrect data. âś… Control It <input name=”email” autocomplete=”email”> <input name=”one-time-code” autocomplete=”one-time-code”> Why Improves UX and security.
CSS position: sticky Not Working? Here’s Why
Sticky fails when parent has: overflow: hidden; âś… Fix Remove overflow or move sticky element higher in the DOM. Sticky only works inside scrollable ancestors.