6 min read The Three Pillars of Observability Observability is the ability to understand the internal state of a system from its external […] Read article
6 min read Core Entities Ticket: ticket_id, customer_id, subject, description, priority (LOW, MEDIUM, HIGH, URGENT), status (OPEN, IN_PROGRESS, WAITING_ON_CUSTOMER, RESOLVED, CLOSED), category, assigned_agent_id, Read article
6 min read When to Use 2D DP 2D DP uses a table dp[i][j] where i and j represent positions in two sequences, Read article
5 min read Core Entities PaymentIntent: intent_id (idempotency key), amount_cents, currency, customer_id, payment_method_id, status (CREATED, PROCESSING, SUCCEEDED, FAILED, CANCELLED), created_at, metadata. PaymentMethod: method_id, Read article
5 min read The Sliding Window Technique for Strings A sliding window maintains a contiguous substring without re-scanning from scratch. Two pointers (left Read article
6 min read Core Entities Post: post_id, user_id, content, media_urls[], platforms[] (TWITTER, INSTAGRAM, LINKEDIN, FACEBOOK), scheduled_at (UTC), status (DRAFT, SCHEDULED, PUBLISHING, PUBLISHED, FAILED), Read article
6 min read Why Distributed Locks? A mutex works within a single process. A database row lock works within a single database. When Read article
6 min read Core Entities Order: order_id, customer_id, restaurant_id, driver_id, items[], total_cents, status, placed_at, estimated_delivery_at. OrderStatus (state machine): PLACED -> CONFIRMED -> PREPARING Read article
6 min read The Problem with Distributed Transactions In a monolith with a single database, ACID transactions guarantee atomicity: either all operations succeed Read article
5 min read What Is a Config Management Service? A configuration management service stores application settings that need to change without a code Read article
6 min read The Core Challenge A flash sale sells a limited quantity (e.g., 1000 units) at a discounted price for a short Read article
6 min read What Is a Geo-Proximity Service? A geo-proximity service finds entities (businesses, drivers, users) near a given location. Core operations: store Read article
5 min read Core Entities Provider: provider_id, name, timezone, working_hours (JSONB: {“MON”: [“09:00″,”17:00”], …}), slot_duration_minutes (e.g., 30). Appointment: appointment_id, provider_id, client_id, start_time (UTC), Read article
6 min read Why Sorting Matters in Interviews Sorting is foundational: dozens of problems become O(n log n) after sorting (two-sum, 3-sum, interval Read article
6 min read Core Entities Content: content_id, type (TEXT, IMAGE, VIDEO), author_id, platform, raw_content / storage_url, created_at. ModerationDecision: decision_id, content_id, verdict (APPROVED, REMOVED, Read article
