Copies and splits of data
Module 7 of the System Design Masterclass. Every lesson here is free to read, with no account.
- 8 lessons
- 2 h 55 min of reading
- 39Replication: leader and followersHow a database keeps copies of its data on other servers, what the copies are for, and what happens when the leader waits for them or does not.24 minCore Fast track
- 40Why do I see old data after saving? (replica lag)Why a follower can show old data right after you save, how long the delay lasts, how to make users see their own changes, and the first plain meaning of eventual.24 minCore Fast track
- 41Failover: what happens to writes in flightWhat happens when the leader dies: how a follower is promoted, which writes can be lost, how long writes stop, and how two leaders at once do harm.24 minCore
- 42Backups and disaster recoveryWhy a follower cannot undo a DELETE, how a backup plus the log restores data to one chosen moment, and what RPO and RTO mean.12 minCore
- 43Sharding: splitting data across serversHow to split one database over several servers: the shard key, range, hash and directory, what a bad key costs, and why adding a shard is hard.24 minCore Fast track
- 44Adding servers without moving all the data (consistent hashing)How a ring of hash positions lets you add or remove a server and move only a small share of the data, and how virtual nodes make the load even.23 minCore Fast track
- 45When one key gets all the traffic (hot partition)Why one very popular key can overload one shard whatever the number of shards, how to find it, and how to split it, copy it or cache it.20 minCore
- 46How databases write fast: LSM trees and Bloom filtersHow a write-heavy database stores data: a log and a table in memory, sorted files that never change, merging in the background, and a Bloom filter that says a key is definitely not in a file.24 minDepth
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