What happens if multiple Consumers are run on one partition, and why can this be problematic?

In Kafka, a single partition can only be consumed by one Consumer from a single Consumer Group at a time. If multiple Consumers are started on the same partition within the same group, only one of them will actually receive messages, while the others will be idle.

Problems:

• No parallel processing within a single partition, as message order must be preserved.
• An excessive number of Consumers on a partition does not increase performance, but only complicates the architecture.

If Consumers belong to different groups, each will receive a copy of the messages, which may be undesirable.

Therefore, to scale consumption, you need to increase the number of partitions rather than running many Consumers on a single partition.