Twitter at Fan-out on write (~5M users) — build it

While this loads — worth knowing

ElastiCache RedisnotElastiCache Memcached

Redis has data structures — sorted sets, counters, pub/sub. Memcached has plain keys and nothing else.

Unlock building Twitter's architecture

Pick a plan to have any design scored against the reference, build every scale from a blank canvas, and play every scale journey.

1 month₹249onceAbout ₹249 a monthA look at the whole thingLong enough to know if it suits you3 months₹599onceAbout ₹200 a monthA focused run at the examMost people pass inside thisMost popular6 months₹1,099onceAbout ₹183 a monthStudying alongside a jobTwice the time of three months, two-thirds more to pay

What you getFreeWith a plan

One scenario, as multiple choice or fill the gaps
Your score, with the reason behind every line
Every scenario, three ways to answer
Building from scratch
An AI review of your answers
An AI check of designs of your own
The shape library

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Every practice plan includes the AI review

An AI review of your answersDesigns you build from scratch, multiple-choice picks and filled-in gaps, each reviewed against the scenario and the choices you actually made. A shared daily allowance — 5 a day on the monthly plan, 10 on the three-month, 15 on the six-month — and a design reviewed before comes back without using one.
Why it works, or why it doesn’tWhether your design meets what the scenario asks, and what in it is wasteful.
What’s needed, and what isn’tEach missing piece named with the reason the scenario needs it, and each extra with what it costs you.
Where you’re laggingA scored breakdown of every service and connection, and the one thing to fix next.
A check of designs of your ownDescribe a system in your own words, draw it, and the AI says whether the drawing does what you described. No score, because nobody wrote an answer key for it. It shares the daily allowance.
Understand how your design breaksFor a design of your own, every failure it can suffer, what each does and where — worked out exactly, and free to read as often as you like. The AI’s read of which ones bite first at your scale shares the daily allowance.
New scenarios, written for you10 a month: a brief nobody has answered before, on a shape you have not practised yet, built from scratch and marked by the same scorer as the rest. Its own allowance, separate from the daily reviews.
Every scenario, three ways to answerBuild from scratch, pick from multiple choice, or fill the gaps in a reference design.
The shape library16 architectures, the signals in a brief that point at each, and what each costs you.