Why can there be one consumer for multiple partitions and when should they be increased?

In message processing systems (e.g., Kafka), one consumer can be assigned to a single partition within a group, but overall, one consumer can be responsible for multiple partitions if there are fewer consumers than partitions. This occurs because each consumer in a group reads data from one or more partitions, but a partition cannot be read simultaneously by multiple consumers within the same group.

When to increase the number of consumers:

• If the message processing load increases and one consumer cannot handle the flow.
• To improve parallelism and processing speed.
• If the number of partitions increases to ensure load balancing.

It is important that the number of consumers does not exceed the number of partitions, otherwise some consumers will be idle.