How many partitions are needed for a consumer group?

The number of partitions in a Kafka topic for a consumer group directly affects the message processing parallelism.

• The maximum number of active consumers in a group cannot exceed the number of partitions, as each partition can only be assigned to one consumer in the group.
• If there are fewer partitions than consumers, some consumers will be idle.
• If there are more partitions than consumers, some consumers will process multiple partitions.

Therefore, for effective operation of a consumer group, the number of partitions should be equal to or greater than the number of consumers to ensure maximum parallelism.

Example: if you have 5 consumers, it is advisable to have at least 5 partitions.