Database / ValKey Interview questions

What is AOF persistence in Valkey?

AOF (Append Only File) persistence logs every write command, in order, to a file as it happens, and rebuilds the dataset by replaying that log on startup.

How aggressively the log is flushed to disk is controlled by appendfsync: always fsyncs after every write for maximum durability, everysec fsyncs roughly once per second as a balance of safety and speed, and no leaves flushing to the operating system.

Because the log only grows, Valkey periodically runs BGREWRITEAOF to compact it into the smallest set of commands that reproduce the current dataset, keeping restart time and disk usage under control.

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AOF persistence rebuilds the dataset on restart by... loading a binary snapshot

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replaying the logged write commands in order

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querying replicas for the data

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downloading a cloud backup

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The appendfsync everysec setting... fsyncs after every single write

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fsyncs the AOF buffer to disk about once per second

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disables fsyncing entirely

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only fsyncs during BGSAVE

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Database / ValKey Interview questions

What is AOF persistence in Valkey?

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