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CodingLevel 3

Error handling

Easy

Medium

Hard

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Error handling & resiliencePreventing a single broken service from bringing down the entire company.3 min Resource leak (handles that never close)Every request opens a handle and forgets to close it, the pool fills until new work is turned away.3 min Connection pool exhaustionA slow dependency quietly holds every connection hostage until new requests have nowhere to go.4 min HTTP connection leaksWhy failing to read the response body will slowly choke your server to death.3 min SQL data accessExtracting exactly what you need, nothing more, nothing less.3 min Blocking accept with no timeoutA server thread that blocks forever on a stalled connection is a thread you'll never get back.4 min Connection pool leaksBorrowing a book from the library and never returning it.3 min File descriptor leaksEvery open() hands back a file descriptor from a finite per-process table, forget to close() and the table fills until the process can open nothing more.5 min Handling a write errorA write isn't done when the function returns, it's done when the data is durable. Until then, never tell the client "saved."4 min HTTP client timeoutsWhy default HTTP clients are dangerous ticking time bombs.3 min HTTP retries without backoffHow 'trying again immediately' accidentally launches a DDoS attack against your own database.3 min HTTP retry idempotencyWhy automatically retrying a failed HTTP POST request might accidentally charge a user's credit card twice.3 min HTTP status ignored (fetch)Why JavaScript's `fetch()` pretends that a 500 Server Error is a massive success.3 min K-fold cross-validationHow to ensure your model didn't just get lucky on the test test.3 min Target leakageWhen your model cheats on the final exam by looking at the answer key.3 min Temp file leaksA temp file is a guest, not a tenant, if nobody shows it the door, it stays forever.3 min Time series validationWhy randomly splitting data will make you lose millions in the stock market.3 min TLS socket without a clean shutdownHanging up by yanking the cable instead of saying goodbye, the other side can't tell whether you finished talking or got cut off, so it keeps the line open just in case.4 min