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Lessons (26)

• N+1 Queries, Loading & Pagination

  … It can turn a 50-row page into 50 times 20 times 10 joined rows. Ask which fields …

• Indexes, EXPLAIN & Query Plans

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

• SQL vs NoSQL Databases

  … no JOIN needed to read it { id: ObjectId("…"), customer: { id: 17, name: "Ana", email: "ana@mail.com" }, items …

• Batch vs Stream and Data Modeling

  … Normalized tables Integrity and flexible writes Reads may join Denormalized read model Measured read path is costly Duplicates …

• Database Relations & Foreign Keys

  … use a join table, never a comma-separated list An enrollment is a relationship with its own facts …

• Arrays & Strings

  … Collect parts in an array and join("") at the end. js // ✅ Efficient string building const parts = []; for (const …

• Views, Triggers & Stored Procedures

  … It can simplify joins, expose a secure subset, and give clients a stable interface. A materialized view stores …

• S — Single Responsibility Principle

  … then(setUser); }, [id]); if (!user) return <Spinner / ; const joined = new Date(user.createdAt).toLocaleDateString("en-GB", { year: "numeric …

• Replication, Partitioning & Sharding

  … Cross-shard joins and transactions are expensive. Prefer colocating related data, asynchronous aggregates and explicit workflows. Do not …

• CQRS & Event Sourcing

  … 10–1000× more Shape Normalised, enforces rules Denormalised, joined, pre-computed Storage Postgres (transactions) Elasticsearch (search), Redis (fast …

• YAGNI: You Aren't Gonna Need It

  … escapeCsv(o.customer)},${o.total} ); return [header, ...rows].join("\n"); } If PDF export is requested next quarter, you …

• Stacks & Queues

  … Queue Operation Meaning Cost (proper queue) --- --- --- enqueue(x) join the back O(1) dequeue() leave the front O …

• Small Functions That Do One Thing

  … user.email, subject: "Welcome!", html: <h1 Hi ${user.email}</h1 <p Thanks for joining.</p , }); return user; } After …

• Hash Maps & Sets

  … const word of words) { const key = [...word].sort().join(""); // "eat" → "aet" if (!groups.has(key)) groups.set(key …

• Deployments, ReplicaSets & Rollouts

  … log collectors, monitoring agents, CNI Adds a pod when a node joins Job Run to completion once: migrations …

• Kafka vs RabbitMQ & the Kafka Ecosystem

  … filtering, mapping, joining streams, windowed aggregations, with exactly-once support. No separate cluster needed; it runs inside your …

• Consumers & Consumer Groups

  … Understand it before relying on it. Rebalancing When a consumer joins , leaves or crashes , the group rebalances : partitions …

• Creational Patterns: How to Make Objects

  … both come from the same factory return [uiFactory.createInput(), uiFactory.createButton()].map((c) = c.render()).join(""); } buildLoginForm(prefersDark …

• Scaling & Health Probes

  … rescues them ( liveness → restart). - "Are you ready to join the relay race?" A swimmer catching their breath sits …

• Finding Service Boundaries with DDD

  … for example, event schemas) Shared kernel A small, jointly owned shared model (use sparingly) mermaid flowchart LR Legacy …

• Scaling, Load Balancing & Rate Limiting

  … all celebrities on one) Cross-shard queries and JOINs Must query every shard and combine the results Re …

• Database Indexing & Transactions

  … keys (automatic), foreign keys, columns in frequent WHERE , JOIN and ORDER BY clauses. Queries that can't use …

• Normalization & Denormalization

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

• Data in Microservices: Sagas & the Outbox Pattern

  … Options: Approach How Trade-off --- --- --- API composition A BFF/gateway calls each service and joins in memory Simple …

• Behavioral Patterns II: Chain, Template, Iterator, Mediator, Memento, Visitor

  … mediator between users class ChatRoom { members = new Map(); join(user) { this. members.set(user.name, user); user.room …

• Domain-Driven Design: Strategic Design

  … Two teams succeed or fail together; they plan jointly Tightly linked features, good collaboration Shared kernel A small …