A topic is a named category of events. Topics are split into partitions — each partition is an ordered, append-only log. Every message in a partition gets a unique, monotonically increasing integer called an offset. Kafka guarantees ordering within a partition but NOT across partitions.
Key configuration
num.partitions (default 1) — topic-level parallelism
retention.ms — how long messages are kept
retention.bytes — size-based retention cap