What happens when my server reads a database row?

A "simple" query is a network round trip, two kernels, a query planner, a buffer pool, a B+ tree and — on a cold cache — an SSD read. Zoom in to see why the same query is 0.2 ms one moment and 40 ms the next.

InputSELECT * FROM users WHERE id = 42A one-line query returns one row in 2 ms. Which machines, kernels, buffers and trees did it touch?
ZoomWhat the ORM shows you: the application asks, the database answers. Both the network and the storage engine are hidden.
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Click a node to see what happens there, what state changes, how it fails, and which lesson explains it. Then zoom to the next level and watch the arrow you clicked expand into its own chain — no step is magic.

Continue with the lessons

The Socket: A Descriptor With Two Kernel Buffers Behind ItFollow send() Through the OS to recv()Connection PoolingFollow a File ReadWhat Happens When the Receiver Is Slow