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Lessons (30)

• Indexes, EXPLAIN & Query Plans

  Design indexes from real filter, join and sort patterns, then prove improvements with query plans and production-like …

• Database Indexing & Transactions

  … smaller and faster Covering ( INCLUDE ) Answer the query from the index alone The cost of indexes Indexes aren …

• Transactions, Indexes & Concurrency

  Interview answers for triggers, ACID, clustered indexes, deadlock/livelock and RAID. Covers PDF questions 8-11 and 18 …

• Hash Maps & Sets

  … The most famous interview question. js function twoSum(nums, target) { const indexOf = new Map(); // value → index for (let …

• Design a Ride-Sharing Service

  Match riders and drivers with a geo index, safely lease availability, and treat location as a fast-changing …

• Database Relations & Foreign Keys

  … Add an index on orders(customer id) when the product frequently loads a customer orders. A foreign key …

• Data Structures for Scale

  Use geospatial indexes and probabilistic structures to make huge queries practical while understanding their error bounds. ![Scale-oriented …

• Arrays & Strings

  … equally sized boxes side by side, reached instantly by index](/img/dsa/array-memory.svg) That's why …

• Database Internals, Replication and Scaling

  … Use indexes and query plans before adding hardware. Replicas increase read capacity but add lag; route read-your …

• SQL Language, Identifiers & Data Types

  … UUIDs can be generated without a central counter and help distributed writes, but cost more index space. Generated …

• Vertical Slice Architecture & the Modular Monolith

  … schema) ├── catalog/ │ └── index.ts export { getProductSnapshot } from "./application/…" └── billing/ └── index.ts ts // modules/catalog/index.ts — the catalog …

• Design a Logging and Monitoring Platform

  … A durable stream absorbs bursts; processors index a bounded hot window and archive older data cheaply. Partition by …

• Binary Search

  … find the first / last position "Find the first index where x appears" in [1, 2, 2, 2, 3 …

• Storage Engines & Database Operations

  … matters A storage engine decides how rows and indexes reach disk. You do not need to implement one …

• Replication, Partitioning & Sharding

  … Do not shard because it sounds scalable; exhaust indexing, caching, replicas and partitioning where appropriate first.

• N+1 Queries, Loading & Pagination

  … id DESC LIMIT 50 Support it with an index matching the filter and sort, such as orders(customer …

• Two Pointers & Sliding Window

  … longestUniqueSubstring(s) { const lastSeen = new Map(); // char → last index let left = 0; let best = 0; for (let right …

• Kafka vs RabbitMQ & the Kafka Ecosystem

  … the easiest way to implement the outbox pattern or to stream database changes to search indexes and warehouses …

• Big-O Notation Made Simple

  … hidden loops Some one-liners hide a loop inside: Code Cost --- --- arr.includes(x) , arr.indexOf(x) O …

• Structural Patterns: How to Connect Objects

  … README.md", 2), new Folder("src", [new File("index.js", 10), new File("app.js", 25)]), ]); project.getSize …

• Stacks & Queues

  … new Array(nums.length).fill(-1); const stack = []; // indexes still waiting for a bigger number for (let i …

• Linked Lists

  … Seriously. Key takeaways - Linked lists trade O(1) index access for O(1) insert/delete at known positions …

• How a Web Request Works

  … keep-alive connections (skip handshakes), caching and database indexes . All covered in later lessons. Key takeaways - DNS finds …

• What Is Apache Kafka?

  … K K -- DB[(DB sync)] K -- SE[Search index] K -- AN[Analytics] K -- MON[Monitoring] end Producers publish …

• React Fundamentals

  … Using the array index as the key causes bugs when items are reordered or removed. State: data that …

• Trees & Binary Search Trees

  … DOM , JSON objects, React component trees, and database indexes (B-trees). Tree vocabulary ![Tree vocabulary: root, parent, child …

• Heaps & Priority Queues

  … No node objects needed: For the node at index i Formula --- --- Parent Math.floor((i - 1) / 2) Left …

• REST API Design

  … c["DB jumps straight there<br/ using the index ⚡"] end Rule 5: Idempotency for unsafe retries ⭐ Networks fail …

• Normalization & Denormalization

  … A query cannot safely join, constrain, index, or update one item inside that string. Good 1NF shape: one …

• Caching & Redis

  … ms In the next room Database with an index ~5 ms Downstairs Slow DB query / external API 100 …