Understanding Kafka Topics and Partitions, Kafka : Use common consumer group to access multiple topics, Kafka consumer offsetForTimes method returns only few partitions offsets position not all, Kafka python client consumer behaviour in case of 1 consumer and multiple partitions. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. However, they can consume from more than one partition at a time. Find centralized, trusted content and collaborate around the technologies you use most. 
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@JaakkoPallari amazing answer! This way the offsets will not overlap between groups. The offsets are stored per partition AND consumer group, i.e. Data Modeling with Kafka? Thank you for the detailed answer, i think i understand better the relationship between groups and partitions. What's inside the SPIKE Essential small angular motor? Consumer groups, as i understand, are abstractions to the idea of partitions and they essentially promise the same thing, two different clients that connect to two different consumer groups of the same topic should consume and commit the same messages without interrupting each other. Therefore, none of the clients in the same consumer group will consume data from the same partition. The same consumer group consumes from 2 different partitions. Kafka guarantees order of messages, right? @Arik I added some more details to my answer based on your comment. 
System Clock vs. Hardware Clock (RTC) in embedded systems. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. The ideas by themselves are pretty clears, each message that's pushed to a topic gets replicated to all of it's partitions, right? As an enthusiast, how can I make a bicycle more reliable/less maintenance-intensive for use by a casual cyclist? Your understanding of consumer groups is correct, but the details in partitions need a bit of clarification. Connect and share knowledge within a single location that is structured and easy to search. The more partitions your topic has, the more clients you can have working in parallel. How does it work with multiple partitions for the same topic? I don't understand how it happens, doesn't it mean that the idea of consumer groups and the idea of partitions contradict one another? I hope this answer makes it more clear on what's going on. How should I deal with coworkers not respecting my blocking off time in my calendar for work? How does it work with multiple partitions for the same topic? What is the difference between Error Mitigation (EM) and Quantum Error Correction (QEC)? Is "Occupation Japan" idiomatic? Multiple consumer groups arrangement is similar to the fan-out pattern. If you have clients in different consumer groups, they can consume from the same partitions. Your observations are correct. I'm having trouble to grasp the relationship behind partitions and customer groups. Making statements based on opinion; back them up with references or personal experience. All of the messages written to the topic will be split between the topic's partitions. 2. 464), How APIs can take the pain out of legacy system headaches (Ep. Thanks for contributing an answer to Stack Overflow! I'll gladly add more details if necessary. Thus, you could say that the multi-partition with single consumer group arrangement works similar to the worker pattern. Not exactly. Thus, each partition will only contain a subset of all the messages written to the topic. In-fact, i've seen for myself that it's not always true, is it true only for a single partition? So as i see it, it should follow that two clients that connect to the same consumer group would consume messages from the same partition Kafka will only allow one client to consume from a partition at a time. and two clients that connect to two different consumer groups would consume from two different partitions (given that there are at least two partitions for that topic) because otherwise the idea of consumer groups doesn't comply with the idea of partitions. Note that replicas are just a way to ensure availability for your data in Kafka cluster in case a Kafka node goes down. A message will be written to a single partition (and its replicas). If the same message appears in two different consumer groups under the same partition, doesn't it mean that the same message was inserted twice to the same partition? Viable alternatives to lignin and cellulose for cell walls and wood? (instead of occupation of Japan, occupied Japan or Occupation-era Japan), Scientific writing: attributing actions to inanimate objects, Scientifically plausible way to sink a landmass. 465). By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Announcing the Stacks Editor Beta release! One question remains in my mind about ordering: if the the node receives message 1 for partition A, message 2 for partition B, and message 3 for partition A. Therefore, all of the consumer groups will receive the same set of data. Thieves who rob dead bodies on the battlefield, Short satire about a comically upscaled spaceship. If a creature with damage transfer is grappling a target, and the grappled target hits the creature, does the target still take half the damage? That way, if two different clients connect to two different partitions of the same topic then they should consume and commit the same messages without interrupting each other. For example, let's assume that you have a topic for all forum post comments. a consumer group can have its own offset for a partition. I still have some things that are unclear to me. What kind of signals would penetrate the ground? 
When i run two clients that consume from different consumer groups (a and b) i get this: Two different consumer groups consume from similar partitions. @payne thanks, glad you found it useful! It does not affect the message processing semantics. What is the difference between String and string in C#? In Apache Kafka why can't there be more consumer instances than partitions? Luckily, messages with the same key will end up in the same partition, so you can guarantee ordering by key. Asking for help, clarification, or responding to other answers. I read that when i commit an offset, it is committed as part of the partition and not the consumer group, so if i commit an offset in one group, will it affect the offset of another if it pulls from the same partition? Why dont second unit directors tend to become full-fledged directors? Also, if you have more clients than partitions in a single group, some of the clients will not get any data at all because there is no partition for them to consume data from. Kafka guarantees order of messages, right? As far as I understand it, message 3 cant be placed before 1 unless the node receives message 3 first. Message ordering can only be guaranteed per partition. Code completion isnt magic; it just feels that way (Ep. Is there any chance that somehow partition A would have had message 3 placed in its queue before message 1? 1. So as i see it, it should follow that two clients that connect to the same consumer group would consume messages from the same partition and two clients that connect to two different consumer groups would consume from two different partitions (given that there are at least two partitions for that topic) because otherwise the idea of consumer groups doesn't comply with the idea of partitions. 
Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. I read that when i commit an offset, it is committed as part of the partition and not the consumer group, so if i commit an offset in one group, will it affect the offset of another if it pulls from the same partition? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. To learn more, see our tips on writing great answers. Since a partition only has a subset of the data and it's only assigned to a single client at a time, each client will consume a unique subset of the data written to the topic. Topics and Partitions. If you end up seeing 3 before 1 in your partition, I suspect that the message producer might write them out of order. If you only care about ordering of comments within a single forum post, you can select the forum post identifier as the message key for all the comments. bash loop to replace middle of string after a certain character. Is a glider on a winch directionally stable? However, when i run a simple consumer client in C#. 
The ideas by themselves are pretty clears, each message that's pushed to a topic gets replicated to all of it's partitions, right? rev2022.7.20.42632. Partitions in Kafka drive the parallelization factor for your message processing. In-fact, i've seen for myself that it's not always true, is it true only for a single partition?
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