As far as I understand it, message 3 cant be placed before 1 unless the node receives message 3 first.
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What's inside the SPIKE Essential small angular motor? Kafka guarantees order of messages, right? a consumer group can have its own offset for a partition. Is there any chance that somehow partition A would have had message 3 placed in its queue before message 1? 1. Why don't they just issue search warrants for Steve Bannon's documents? In-fact, i've seen for myself that it's not always true, is it true only for a single partition? System Clock vs. Hardware Clock (RTC) in embedded systems. zookeeper producer consumer Is "Occupation Japan" idiomatic? Is a glider on a winch directionally stable? The offsets are stored per partition AND consumer group, i.e. 
kafka partitions redis logz aggregation capabilities 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. How does it work with multiple partitions for the same topic? I still have some things that are unclear to me. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. 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. I hope this answer makes it more clear on what's going on. It does not affect the message processing semantics. How does it work with multiple partitions for the same topic?
I'll gladly add more details if necessary. 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. Topics and Partitions. Announcing the Stacks Editor Beta release! In-fact, i've seen for myself that it's not always true, is it true only for a single partition? The ideas by themselves are pretty clears, each message that's pushed to a topic gets replicated to all of it's partitions, right? Kafka guarantees order of messages, right? What kind of signals would penetrate the ground? 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. I'm having trouble to grasp the relationship behind partitions and customer groups. 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? In Apache Kafka why can't there be more consumer instances than partitions? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. bash loop to replace middle of string after a certain character. 465). If you have clients in different consumer groups, they can consume from the same partitions. Viable alternatives to lignin and cellulose for cell walls and wood? However, when i run a simple consumer client in C#. Thus, you could say that the multi-partition with single consumer group arrangement works similar to the worker pattern. Multiple consumer groups arrangement is similar to the fan-out pattern. 464), How APIs can take the pain out of legacy system headaches (Ep. What is the difference between String and string in C#? Thus, each partition will only contain a subset of all the messages written to the topic. All of the messages written to the topic will be split between the topic's partitions.
kafka partition Luckily, messages with the same key will end up in the same partition, so you can guarantee ordering by key. Making statements based on opinion; back them up with references or personal experience. rev2022.7.20.42632. Therefore, all of the consumer groups will receive the same set of data. Therefore, none of the clients in the same consumer group will consume data from the same partition. If you end up seeing 3 before 1 in your partition, I suspect that the message producer might write them out of order. Not exactly. The more partitions your topic has, the more clients you can have working in parallel. This way the offsets will not overlap between groups. Find centralized, trusted content and collaborate around the technologies you use most. 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. 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. @JaakkoPallari amazing answer! 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? 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? What is the difference between Error Mitigation (EM) and Quantum Error Correction (QEC)?
Note that replicas are just a way to ensure availability for your data in Kafka cluster in case a Kafka node goes down. Data Modeling with Kafka? The same consumer group consumes from 2 different partitions. 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. Message ordering can only be guaranteed per partition. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 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? kafka producer concepts broker acknowledgements wait doesn How should I deal with coworkers not respecting my blocking off time in my calendar for work? 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. Thanks for contributing an answer to Stack Overflow! kafka binder spring cloud stream reference docs apache figure io htmlsingle guide github 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. Your understanding of consumer groups is correct, but the details in partitions need a bit of clarification. 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? kafka advantages A message will be written to a single partition (and its replicas). Thieves who rob dead bodies on the battlefield, Short satire about a comically upscaled spaceship. Asking for help, clarification, or responding to other answers. For example, let's assume that you have a topic for all forum post comments. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. @Arik I added some more details to my answer based on your comment. 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. Your observations are correct. Code completion isnt magic; it just feels that way (Ep. @payne thanks, glad you found it useful! Why dont second unit directors tend to become full-fledged directors? Partitions in Kafka drive the parallelization factor for your message processing. 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? 2. (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. To learn more, see our tips on writing great answers. 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. Thank you for the detailed answer, i think i understand better the relationship between groups and partitions. However, they can consume from more than one partition at a time.
