Why do brokers in Pulsar not store data locally?

Keeping brokers stateless is a deliberate architectural choice: it decouples the availability and durability of message data from the lifecycle of any individual broker process, so a broker can be restarted, replaced, or moved without any risk to stored data.

All durability responsibility is delegated to BookKeeper, whose bookies replicate every entry across an ensemble according to configured quorum settings, so data survives broker churn entirely independent of how brokers come and go.

This also simplifies broker-level operations like rolling upgrades and autoscaling, since adding or removing broker capacity is purely a compute decision with zero data rebalancing implications.

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