Posts about databases
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.