Backend - Mahdi Molavi | Senior Backend Engineer & Tensor Researcher https://mahdimolavi.ir/ en Backend - Mahdi Molavi | Senior Backend Engineer & Tensor Researcher DataLife Engine Backend Notes 2: Adaptive Testing with IRT Behind an API https://mahdimolavi.ir/backend-notes/25-backend-notes-2-adaptive-testing-irt-item-selection-api.html https://mahdimolavi.ir/backend-notes/25-backend-notes-2-adaptive-testing-irt-item-selection-api.html Backend Notes 2: Adaptive Testing with IRT Behind an API

How an IRT-based adaptive test picks every next question: 1PL to 3PL models, EAP ability estimates, maximum information with exposure control and content balancing, and an API that stays responsive at exam peaks.

]]> admin Mon, 12 Oct 2026 10:00:00 +0330 Real Watch Time from Noisy Video Player Logs https://mahdimolavi.ir/backend-notes/33-real-watch-time-from-noisy-video-player-logs.html https://mahdimolavi.ir/backend-notes/33-real-watch-time-from-noisy-video-player-logs.html Real Watch Time from Noisy Video Player Logs

Video players send play, pause, seek and heartbeat events, and some of them never arrive. How I turned that noisy telemetry into reliable per-learner watch-time facts with .NET 10 and SQL Server.

]]> admin Mon, 05 Oct 2026 11:27:45 +0330 Backend Notes 1: Redis Sentinel for Up to 70,000 Exam-Day Users https://mahdimolavi.ir/backend-notes/23-backend-notes-1-redis-sentinel-exam-day-traffic.html https://mahdimolavi.ir/backend-notes/23-backend-notes-1-redis-sentinel-exam-day-traffic.html Backend Notes 1: Redis Sentinel for Up to 70,000 Exam-Day Users

Exam platforms idle for weeks, then everyone starts at once. Redis Sentinel failover, StackExchange.Redis configuration, stampede-safe caching and Locust load tests, from a setup that carried 45,000 to 70,000 concurrent users.

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