Core conceptsThe ring
How does every client find a key’s server without asking anyone?
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More questions.
Networking and APIsFailover
Your TTL is 60 seconds. Why does DNS failover take 150?
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Data and storageB+tree
How do five page reads find one payment among 500 million rows?
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Caching fundamentalsRedis
Your Redis cache filled up and started refusing writes. Why?
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Messaging and streamsPoison messages
Why can one bad message freeze a whole Kafka partition?
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Distributed coordinationCRDTs
Mumbai counted 10 likes, Delhi 13. Why is the true total 15?
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Running in productionGray failure
How did broken Amazon servers win more traffic than healthy ones?
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Why is it slow? Performance anti-patternsDetect it
Nobody touched login. Why did it go from 3 ms to 21?
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Multi-tenant SaaSLate events
Usage from 31 October arrives on 1 November. Which month’s invoice gets it?
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Architecture stylesDHT lookup
No index, 10 million peers. How do you find a file in 24 hops?
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System design trade-offsEvent loops
Why does one 1.3-second JSON parse freeze every other user?
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Key technologiesStalled watermark
Clicks keep flowing, yet no window ever fires. What’s holding time back?
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Common patternsFlash sale
100,000 taps for 500 berths at 10 am. What should most requests see?
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InfrastructureDurability
How can one leader crash silently lose 14,000 acknowledged payments?
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Search & discoveryPartitioning
Why can 100 polite crawlers add up to one rude one?
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Storage & mediaDisk heat
Why do bigger hard drives make S3’s job harder, not easier?
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Social & feedsComments
One upvote, no downvotes. Why isn’t that the best comment?
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Real-time & collaborationTies
Two players hit 48,250 points. Who should rank first?
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Location & mapsTiles
1.6 million tile fetches a second at peak. Who draws them?
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E-commerce & bookingMatching
100 million alerts, one price drop. How do you find the ones that fire?
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Data, analytics & monitoringSnapshots
How do you copy a 2-billion-row table while it keeps changing?
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AI & LLM systemsKV cache
Why does reserving room for long answers fit 51 chats, not 233?
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Core conceptsPick two?
Why can’t you just “pick two” of consistency, availability and partition tolerance?
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Networking and APIsLongest prefix
Four routes match one packet. How does a router pick?
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Data and storageColumn order
Why does an indexed passbook read 4,789 table pages to show 20 payments?
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Caching fundamentalsDead nodes
One of 20 cache nodes dies at peak. Why does the database brown out?
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