- All Implemented Interfaces:
- org.apache.kafka.clients.consumer.internals.PartitionAssignor
public class RoundRobinAssignor
extends org.apache.kafka.clients.consumer.internals.AbstractPartitionAssignor
The round robin assignor lays out all the available partitions and all the available consumers. It
then proceeds to do a round robin assignment from partition to consumer. If the subscriptions of all consumer
instances are identical, then the partitions will be uniformly distributed. (i.e., the partition ownership counts
will be within a delta of exactly one across all consumers.)
For example, suppose there are two consumers C0 and C1, two topics t0 and t1, and each topic has 3 partitions,
resulting in partitions t0p0, t0p1, t0p2, t1p0, t1p1, and t1p2.
The assignment will be:
C0: [t0p0, t0p2, t1p1]
C1: [t0p1, t1p0, t1p2]
When subscriptions differ across consumer instances, the assignment process still considers each
consumer instance in round robin fashion but skips over an instance if it is not subscribed to
the topic. Unlike the case when subscriptions are identical, this can result in imbalanced
assignments. For example, we have three consumers C0, C1, C2, and three topics t0, t1, t2,
with 1, 2, and 3 partitions, respectively. Therefore, the partitions are t0p0, t1p0, t1p1, t2p0,
t2p1, t2p2. C0 is subscribed to t0; C1 is subscribed to t0, t1; and C2 is subscribed to t0, t1, t2.
That assignment will be:
C0: [t0p0]
C1: [t1p0]
C2: [t1p1, t2p0, t2p1, t2p2]