December 2023
Intermediate to advanced
464 pages
12h 35m
English
Content preview from Patterns of Distributed Systems
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Chapter 3
Write-Ahead Log
Provide durability guarantee without the storage data structures to be flushed to disk, by persisting every state change as a command to the append only log.
Also known as: Commit Log
Problem
Strong durability guarantee is needed even in the case of the server machines storing data failing. Once a server agrees to perform an action, it should do so even if it fails and restarts losing all of its in-memory state.
Solution
Store each state change as a command in a file on a hard disk (Figure 3.1). A single log is maintained for each server process. It is sequentially appended. A single log, appended sequentially, simplifies handling of logs at restart and the subsequent online operations (when the log is appended with ...