Integration / Apache Pulsar Interview questions

What is the difference between persistent and non-persistent topics?

Persistent topics durably store every message in BookKeeper before acknowledging the publish, so data survives broker restarts, and slow consumers can catch up later from the retained backlog.

Non-persistent topics keep messages only in broker memory and never touch BookKeeper, trading that durability for lower publish latency and zero storage overhead - a broker restart loses any in-flight messages with no way to recover them.

Because of this, non-persistent topics suit only data where occasional loss is acceptable in exchange for speed, while persistent topics are the default choice for anything that must not silently disappear.

Persistent	Non-persistent
Stored durably in BookKeeper	Held only in broker memory
Survives broker restarts	Lost on broker restart
Higher publish latency, durable	Lower latency, not durable

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Which topic type survives a broker restart? Non-persistent

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Persistent

✓ Correct! Well done.

neither

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Non-persistent topics trade away durability for: lower publish latency

✓ Correct! Well done.

stronger ordering guarantees

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built-in schema validation

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