ReadKafkaP is used to consume items from one or more Kafka topics. It
uses the Kafka consumer API and consumer groups to distribute partitions
among processors where each partition is consumed by a single processor
at any given time. The reader emits items of type Map.Entry<K,V> where
the key and the value are deserialized using the key/value deserializers
configured in Kafka properties.
Ideally, the total partition count in Kafka should be at least as large
as the total parallelism in the Jet cluster
(localParallelism*clusterSize) to make sure that each processor will
get some partitions assigned to it.
Internally, a KafkaConsumer is created per Processor instance using
the supplied properties. All processors must be in the same consumer
group supplied by the group.id property. It is required that the
group.id is explicitly set by the user to a non-empty value. The
supplied properties will be passed on to each KafkaConsumer instance.
These processors are only terminated in case of an error or if the
underlying job is cancelled.
ReadKafkaP forces the enable.auto.commit property to be set to
false, and commits the current offsets after they have been fully
emitted.