Consumer groups in Kafka allow you to:
- Group consumers by their function in a system.
- Split the processing load of a topic by sharing its partitions between consumers in a group.
What is a consumer group in Kafka?
Why is Kafka so popular?
How many partitions are there in Kafka?
What is load balancing in Kafka?
How many consumers read each partition in a topic?
Can a consumer read from more than one partition?
Can a producer subscribe to more than one channel?
See 4 more
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What is the need of consumer group in Kafka?
Kafka assigns the partitions of a topic to the consumer in a group, so that each partition is consumed by exactly one consumer in the group. Kafka guarantees that a message is only ever read by a single consumer in the group. Consumers can see the message in the order they were stored in the log.
Is consumer group mandatory in Kafka?
The consumer group-id is mandatory, it plays a major role when it comes to scalable message consumption. To start a consumer group-id is mandatory.
How consumer group works in Kafka?
Kafka consumers are typically part of a consumer group . When multiple consumers are subscribed to a topic and belong to the same consumer group, each consumer in the group will receive messages from a different subset of the partitions in the topic.
What is difference between consumer and consumer group?
A consumer group is a group of multiple consumers which visions to an application basically. Each consumer present in a group reads data directly from the exclusive partitions. In case, the number of consumers are more than the number of partitions, some of the consumers will be in an inactive state.
Can multiple consumer groups same topic?
A topic can be consumed by many consumer groups and each consumer group will have many consumers. A topic is divided into multiple partitions. A consumer in a consumer group is assigned to a partition. Only one consumer is assigned to a partition.
How many consumers can Kafka handle?
While Kafka allows only one consumer per topic partition, there may be multiple consumer groups reading from the same partition.
How many consumer groups can be created in Kafka?
By default, the quota for consumer groups is twice the quota for topics. For example, if you can create a maximum of 50 topics on your Message Queue for Apache Kafka instance, you can create a maximum of 100 consumer groups on the instance.
What is a consumer group?
noun. /kənˈsjuːmə ɡruːp/ /kənˈsuːmər ɡruːp/ an organization that makes sure the goods and services people buy or use are safe and that consumers are treated fairly.
Can Kafka consumer listen to multiple topics?
Yes, Kafka's design allows consumers from one consumer group to consume messages from multiple topics.
What if Kafka consumer goes down?
Consumer offset is recorded in Kafka so if the consumer processing the partition in the consumer group goes down and when the consumer comes back, the consumer will read the offset to start reading the messages from the topic from where it is left off. This avoids duplication in message consumption.
Can a Kafka consumer read from multiple partitions?
If the number of partitions is greater, some consumers will read from multiple partitions, which should not be an issue unless the ordering of messages is important.
How many partitions can a Kafka topic have?
Cluster guidelines A Kafka cluster should have a maximum of 200,000 partitions across all brokers when managed by Zookeeper. The reason is that if brokers go down, Zookeeper needs to perform a lot of leader elections. Confluent still recommends up to 4,000 partitions per broker in your cluster.
What if Kafka consumer goes down?
Consumer offset is recorded in Kafka so if the consumer processing the partition in the consumer group goes down and when the consumer comes back, the consumer will read the offset to start reading the messages from the topic from where it is left off. This avoids duplication in message consumption.
What is consumer group in event hub?
A consumer group is a view (state, position, or offset) of an entire event hub. Consumer groups enable multiple consuming applications to each have a separate view of the event stream, and to read the stream independently at their own pace and with their own offsets.
When a consumer wants to join a consumer group it will send request to group coordinator?
When a consumer wants to join a group, it sends a request to the coordinator. The first consumer to participate in a group becomes a leader. All other consumers joining later becomes the members of the group. So, we have two actors, A coordinator, and a group leader.
When a consumer in a consumer group fails the partitions it was assigned with will be transferred to another consumer in the consumer group which is called a _?
Membership in a consumer group is maintained dynamically: if a process fails, the partitions assigned to it will be reassigned to other consumers in the same group. Similarly, if a new consumer joins the group, partitions will be moved from existing consumers to the new one.
What is consumer group?
A consumer group is a group of consumers (I guess you didn’t see this coming?) that share the same group id. When a topic is consumed by consumers in the same group, every record will be delivered to only one consumer. As the official documentation states: “If all the consumer instances have the same consumer group, then the records will effectively be load-balanced over the consumer instances.”
What happens when another consumer joins the same group?
A single consumer in a consumer group. After another consumer joins the same group, each consumer would continue consuming only one partition. Multiple consumers in one consumer group.
What happens when a new consumer is started?
When a new consumer is started it will join a consumer group (this happens under the hood) and Kafka will then ensure that each partition is consumed by only one consumer from that group. So, if you have a topic with two partitions and only one consumer in a group, that consumer would consume records from both partitions.
What does it mean when a consumer stores an offset?
This enables consumers to always know which record should be consumed next from a given partition. Since the consumer offset is stored in Kafka, it means that the position of the consumer group is maintained even after restarts.
What happens if you have more consumers in a group than you have partitions?
If you have more consumers in a group than you have partitions, extra consumers will sit idle, since all the partitions are taken. If you know that you will need many consumers to parallelize the processing, then plan accordingly with the number of partitions. Additional consumers in a group sit idly. When we talked about topics and partitions, I ...
How to send a message to a group?
When sending messages in a distributed setup using a messaging system, you typically have two scenarios you want to achieve. Either you want to: 1 send a message to a targeted group of consumers (which might be just one consumer) or 2 broadcast the message to all the consumers
Can all consumer instances have the same consumer group?
As the official documentation states: “If all the consumer instances have the same consumer group, then the records will effectively be load-balanced over the consumer instances.”. This way you can ensure parallel processing of records from a topic and be sure that your consumers won’t be stepping on each other toes.
What is a consumer in Kafka?
A consumer is the one that consumes or reads data from the Kafka cluster via a topic. A consumer also knows that from which broker, it should read the data. The consumer reads the data within each partition in an orderly manner. It means that the consumer is not supposed to read data from offset 1 before reading from offset 0.
How does Kafka work?
Apache Kafka provides a convenient feature to store an offset value for a consumer group. It stores an offset value to know at which partition, the consumer group is reading the data. As soon as a consumer in a group reads data, Kafka automatically commits the offsets, or it can be programmed. These offsets are committed live in a topic known as __consumer_offsets. This feature was implemented in the case of a machine failure where a consumer fails to read the data. So, the consumer will be able to continue reading from where it left off due to the commitment of the offset.
Why are both consumers of Group 1 and Group 2 in an active state?
Both the consumers of Group 1 will remain in an active state because they are reading the data parallelly. On the other hand, Consumer 1 of Group 2 is also reading the data from Partition 1 under Topic-T.
What does it mean when a consumer reads data from a consumer group?
In the below figure, a consumer from a consumer group is reading the data. After reading the data, the consumer has committed the offset. It means next time, the consumer will read data not from the beginning but from the committed point. Also, somehow the consumer dies, it will be able to continue from the committed state only.
What happens if you lose an active consumer?
Somehow, if we lose any active consumer within the group then the inactive one can takeover and will come in an active state to read the data.
Is consumer 3 inactive?
Thus, Consumer 3 will remain in an inactive state until any of the active consumer leaves. Note: In Example 2, three consumers are present in one group only. That's why Consumer 3 is inactive. However, if the consumer is present in another group, it will be in an active state and able to read the data.
Can a consumer read multiple brokers at the same time?
Also, a consumer can easily read data from multiple brokers at the same time. For example, two consumers namely, Consumer 1 and Consumer 2 are reading data. Consumer 1 is reading data from Broker 1 in sequential order. On the other hand, Consumer 2 is simultaneously reading data from Broker 2 as well as Broker 3 in order.
Do all consumers use the same group ID?
Yes, if all consumers use the same group id, messages in a topic are distributed among those consumers. In other words, each consumer will get a non-overlapping subset of the messages. Having more consumers in the same group increases the degree of parallelism and the overall throughput of consumption. On the other hand, if each consumer is in its ...
Does Kafka have load balanced messages?
I'm working with Apache Kafka and its Java client and I see that messages are load balanced across different Kafka Consumers belonging to the same group (i.e. sharing the same group id).
Is group ID mandatory in Java?
No, groupId seems to be mandatory for Java client starting Kafka 0.9.0.x consumers. You can refer to this JIRA: https://issues.apache.org/jira/browse/KAFKA-2648
Do you need a consumer group to consume all messages?
Don't want to repeat other answers, but just to point out something: You don't actually need a consumer group to consume all messages. The Kafka ConsumerAPI (assuming we're dealing with the Java one) has both a subscribe()and an assign()method. If you want all consumers to receive all messages without load balancing (which is what essentially consumer groups are for), you can just invoke assign()on all consumers, passing it all the partitions for the topic, optionally followed by seek()to set the offsets; that way your consumers will get all messages.
Does Kafka manage partitions?
This way Kafka will not manage partition assignment and will not persist offsets — the consumer is responsible for all that. Depending on your use case, it may be a better approach comparing to having a consumer group per consumer.
Does Kafka have a consumer group?
The kafka consumer will not have any consumer group. Instead you will get this error : The configured groupId is invalid
What is a consumer group in Kafka?
Kafka consumer group is basically several Kafka Consumers who can read data in parallel from a Kafka topic. A Kafka Consumer Group has the following properties: All the Consumers in a group have the same group.id. Only one Consumer reads each partition in the topic. The maximum number of Consumers is equal to the number of partitions in the topic.
Why is Kafka so popular?
Although it is based on the publish-subscribe model, Kafka is so popular because it has the advantages of a messaging queue system. As discussed earlier, if we have a Consumer group, Kafka ensures that each message in a topic is read-only once by a Consumer (Which is similar to a Message Queue system).
How many partitions are there in Kafka?
Let’s assume that we have a Kafka topic, and there are 4 partitions in it. Then we can have the following scenarios: 1. Number of consumers = Number of partitions. In this case, each Consumer will read data from each partition, which is the ideal case. 2.
What is load balancing in Kafka?
Load Balancing: Kafka shares the partitions fairly with each Consumer, thereby making the process of data consumption smooth and efficient.
How many consumers read each partition in a topic?
Only one Consumer reads each partition in the topic.
Can a consumer read from more than one partition?
A Consumer can read from more than one partition.
Can a producer subscribe to more than one channel?
In this model, the messages published by a Producer can be subscribed by more than one Consumer. The Producer and the Consumer are decoupled to a large extent. This model ensures that each Consumer will receive messages on a topic in the producer’s exact order. A typical example may be a dish TV which publishes different channels like music, movie, sports, etc., and the consumers can subscribe to more than one channel. As there are multiple subscribers to a topic, scaling the processing of streams is a challenge.
