← Interview Brush-Up

Interview Brush-Up

System Design Concepts

The building blocks behind every design round, and how they are really built.

When calls fail

Timeouts
Every remote call needs one, and timed out doesn’t mean failed.
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Retries
Back off, add jitter, cap the attempts, or your retries take the service down.
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Idempotency
Same request twice, effect once: an idempotency key makes retries safe.
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Scaling and state

Stateless vs stateful
Keep no user data on the server, so any server can take any request.
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Concurrency vs parallelism
Concurrency keeps many tasks moving with what you have; parallelism adds workers to run them at once.
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Uptime and releases

Databases

When an index gets ignored
A function on the column, a leading wildcard, the wrong type, the wrong column order, or a query that wants most of the table.
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