All 7 Persistence (RDB/AOF) questions
More in Persistence (RDB/AOF)
What is RDB persistence in Redis, and how does it work? What is AOF, or append only file, persistence, and how does it differ from RDB snapshots? What is AOF rewriting, and why is it necessary as an append only file grows over time? What happens if Redis's persistence files, whether RDB or AOF, become corrupted, and how would you attempt to recover? How would you design a persistence strategy that combines both RDB and AOF to get the benefits of both approaches? What happens during Redis startup regarding data loading, and how does the choice between RDB and AOF affect startup time for a large dataset?
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Redis › Persistence (RDB/AOF)

What are the different appendfsync options available for AOF persistence, and how do they balance durability against performance?

Intermediate

Answer

The always option writes and flushes to disk after every single write command, providing the strongest durability but the slowest performance, everysec flushes to disk once per second, offering a reasonable balance most applications choose by default, and no relies on the operating system to decide when to flush, offering the best performance but the weakest durability guarantee.
CONFIG SET appendfsync everysec -- a common balanced default
Real-world example A team evaluating their durability requirements chooses the everysec setting as a reasonable balance, accepting the small risk of losing up to one second of writes during a crash in exchange for meaningfully better performance than the always option.

Common follow-ups: How much data could actually be lost with the everysec setting during a crash?;When would the always setting actually be necessary despite its performance cost?

Redis Backup & Disaster Recovery;Redis Performance Tuning & Benchmarking
All 7 Persistence (RDB/AOF) questions