Blog
System breakdowns of apps you use every day, notes on how we build the courses, and news. A new System breakdown most weeks.
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System breakdown: why a refund takes days when the payment took seconds
You cancel an order and the app says the refund has started. Your bank shows nothing for days. Here is where the money is in between, and which parts of the delay a shop can and cannot change.
System breakdown: why the 'order placed' screen sometimes lies
The app says your order is placed. Four minutes later it says one item is gone. Here is what the first screen really means, and how a well-built system keeps that promise honest.
System breakdown: how a flash sale doesn't melt the database
At 6 pm, 500 bags of rice go on sale at half price and thousands of people press Buy in the same few seconds. Here is how the system sells exactly 500, stays up for everyone else, and says no fast.
Read a query plan in 10 minutes
EXPLAIN output looks like noise until you know the four things to look for. Open the SQL Lab, run one slow query from Mangrove's orders page, and learn to read the plan, fix it, and prove the fix.
Switching from QA to developer: a 16-week plan
You already think in edge cases and know the product better than most developers. Here is a week-by-week plan that turns that into developer skills, at about six hours a week, with free courses and labs.
The practice labs are open: what's free and what's in Plus
Six labs are live on the practice hub: SQL, Code, System Design Studio, Security, QA, and DevOps & TechOps. Here is what each one does, exactly what the free plan includes, what Plus adds, and what is still coming.
Find your system's limit before your users do
A design that works at today's traffic tells you little about next month's. In 15 minutes in the System Design Studio, you can find where a design breaks, what breaks first, and what one more user costs.
What a data analyst actually does in week one
Less modelling, more asking what a number means. A day-by-day look at a new analyst's first week at Mangrove Market, and the skills that week actually uses.
System breakdown: the rider dot that moves across your map
A delivery app shows the rider moving toward your door every few seconds. Here is the path one location update takes, and the three choices that keep it cheap.
Why every lesson has a podcast episode
Many of our learners study on a bus, in a car or after a long shift. Here is how the two-voice episodes work, why the page follows along, and what we learned building them.
System breakdown: what stops a double charge when you tap Pay twice
The network drops just after you press Pay with your mobile wallet. You press again. Here is how a well-built checkout makes sure you pay once.