GuideTechnology
15 min read
Why a query over millions of rows can take seconds or milliseconds depending on one index. Learn how B-tree indexes work, why they stay shallow, composite index column order, covering and partial indexes, selectivity, reading a query plan at a high level, why indexes are sometimes ignored, and what every index costs on writes.
GuideTechnology
17 min read
How to model data for a system design: tables, primary and foreign keys, constraints, one-to-many and many-to-many relationships, normalisation and deliberate denormalisation, ACID transactions, choosing id formats, and designing the model around access patterns. Also covers connection pooling, the N+1 problem and safe schema changes.
GuideTechnology
18 min read
Why queues exist and how they work: producers, consumers and brokers, acknowledgements and redelivery, visibility timeouts, retries, dead-letter queues, ordering, and delivery guarantees. Compares work queues, pub/sub and event streams such as Kafka, and shows how to design background workers that are safe to run twice.
GuideTechnology
17 min read
How large files are stored and delivered: object storage concepts (buckets, keys, durability, consistency, lifecycle), direct uploads with presigned URLs and multipart upload, and CDNs (edge caching, cache keys, TTLs, invalidation versus versioned URLs, static versus dynamic content, private content). Includes a compact file-storage-and-sharing design.
GuideTechnology
20 min read
Caching as a design decision: where caches live, hit ratios, cache-aside, read-through, write-through and write-back, TTLs and invalidation, LRU and other eviction policies, cache stampedes, hot keys, negative caching and distributed caches such as Redis, with the trade-off between faster reads, stale data and invalidation complexity.
GuideTechnology
18 min read
Why load balancers exist, how they spread traffic across servers, and what makes that possible: stateless services. Covers Layer 4 versus Layer 7, reverse proxies, round robin, weighted, least connections and hashing, health checks, draining, sticky sessions, redundancy of the load balancer itself, and autoscaling.
GuideTechnology
15 min read
Turn request rates into the numbers that shape an architecture: storage per day and per year with replication and retention, ingress and egress bandwidth in Gbps, cache memory from the working set, database write limits, and a first server count with headroom and zone failure. Includes a full worked example and a calculator.
GuideTechnology
16 min read
Capacity estimation from absolute basics: units and powers of two, seconds in a day, and the funnel from total users to MAU, DAU, requests per day, average QPS and peak QPS. Includes peak factors you can derive, read and write splits, fan-out, three worked examples and a small calculator.
GuideTechnology
17 min read
When should a caller wait for an answer, and when should work happen later? Learn the costs and benefits of synchronous calls and asynchronous processing, the patterns for returning results later (202 and status polling, webhooks, push), and how to choose between short polling, long polling, Server-Sent Events, WebSockets and mobile push.
GuideTechnology
19 min read
Design APIs that clients can rely on: resources and URLs, HTTP methods and which are safe to retry, status codes, validation, error formats, cursor pagination, filtering, idempotency keys, rate-limit responses, versioning, and when gRPC or GraphQL fit better than REST.
GuideTechnology
17 min read
Follow one request from a phone to a database and back: DNS lookup, TCP and TLS handshakes, HTTP, the edge, the load balancer, the application and the data stores. Learn where the time goes, why round trips and distance dominate latency, and where requests fail.
GuideTechnology
19 min read
How to turn a vague prompt such as "design a photo app" into requirements you can design for: functional requirements, clarifying questions, and non-functional requirements stated as numbers, including latency percentiles, throughput, availability nines, durability and consistency.
GuideTechnology
18 min read
What system design actually is, why interviews test it, the components you will meet and the problem each one solves, and the seven-phase method this 45-article course uses for every design, from a first single-server app to large distributed systems.
CourseTechnology
6 min read
A free, 45-article course that takes you from basic web and backend ideas to designing and defending real systems in SDE-1 and SDE-2 interviews. It teaches a repeatable method (requirements, estimation, APIs, data, baseline, scaling, hardening), the building blocks and distributed-systems fundamentals behind it, and 15 progressively harder case studies.
GuideTechnology
13 min read
A realistic 30-day plan to put this course into practice with free tools and 30 to 45 minutes a day, followed by a long-term roadmap that builds durable skills such as verification, workflow design and evaluation, and a way to keep up as AI changes without chasing every announcement.
GuideCareer
11 min read
Job postings are data. This article shows how to turn a handful of them into a requirements table, compare it honestly with what you can already show, plan a realistic learning path and choose portfolio projects that prove real skills, with AI doing the sorting and you doing the judging and the learning.
GuideTechnology
12 min read
A free, 35-article course on using modern AI well: what it is, how to ask, how to check it, and how to build habits that survive the next product update. This first article explains what to expect and introduces the six-step Work Loop you will use throughout.
GuideTechnology
15 min read
What data structures and algorithms are, why employers test them, what you can honestly expect from this free 28-article course, and the repeatable six-step loop you will use on every problem.
