1.
Brought to you by
Understanding Apache
Kafka Latency at Scale
Pere Urbon Bayes
Senior Solutions Architect -
Professional Services

2.
Pere Urbon Bayes
Senior Solutions Architect - Professional Services at Confluent
■ Working “in computers” since the year 2000
■ Interested in all things Programming, Performance and Security
■ Lego enthusiast and Handball fan
■ Work side by side with customers implementing the most
critical data in motion projects

3.
Agenda for today
Today we are going to cover:
● How to model latency in Apache Kafka and the existing tradeoff
● How to effectively measure Apache Kafka latency
● What you can do as a user to optimise your deployment effectively

4.
Tales of Apache Kafka Latency

5.
Tales of Apache Kafka latency
Measuring performance and latency in distributed systems is certainly not an easy
task, way to many moving parts.
What are the most important properties to consider in Apache Kafka:
● Durability, Availability, Throughput and for sure Latency
NOTE: It is not possible to really achieve great values in all of them!

6.
The different latencies of Apache Kafka
Apache Kafka is a distributed system and many “latencies” can be measured

7.
Produce time
The time since the application produces a
record (KafkaProducer.send()) until a request
containing the message is send to an Apache
Kafka Broker.
Important configuration variables:
● batch.size
● linger.ms
● compression.type
● max.inflight.requests.per.connection

8.
Produce time
By default the producer is optimised for latency.
Batching can improve throughput, but could
introduce an artificial delay.
A batch might need longer waiting time if the
broker has reached
max.inflight.requests.per.connection.
The use of compression might help with
throughput and latency.

9.
The time between when the producer send a
batch of messages to when the corresponding
message gets append to the log (leader).
Time include:
● network and io processing
● queue time (request and response queue)
With low load, usually most of the time is in
network and IO.
As the brokers become more load, queue time
usually dominate.
Publish time

10.
Kafka consumers can only read messages from
fully replicated messages. This time accounts
for all the time necessary for a message to land
in all in sync replicas.
Important configuration variables
● replica.fetch.min.bytes
● replica.fetch.wait.max.ms
Commit time

11.
The time that takes a record to commit is equal
to the time it takes the slowest in-sync follower
to replicate.
The default configuration is optimised for
latency.
Commit times are usually impacted by
replication factor and load.
Commit time

12.
The time it takes for a record to be fetched from
a partition, in Java a successful call to the
KafkaConsumer.poll() method.
Important configuration variables
● fetch.min.bytes
● fetch.wait.max.ms
The default configuration is optimised for
latency.
Fetch time

13.
The distributed system fallacy

14.
The impact of the tradeoffs …..

15.
Durability vs Latency

16.
Acknowledgements (acks)
If the broker become slower at giving back acknowledgements it usually decrease
the producing throughput as it will increase the waiting time
(max.in.flight.request.per.connection).
Using acks=all usually mean increasing the number of producers.
Configuring min.in.sync.replicas is important for availability, however it is not relevant
for latency as replication will happen for all in-sync replicas not impacting the
commit time.

17.
Copyright 2021, Confluent, Inc. All rights reserved. This document may not be reproduced in any manner without the express written permission of Confluent, Inc.
Throughput vs Latency, the eternal question

18.
Improving batching without artificial delays
When applications produce messages that are not send to the same partitions
this will affect batching as they could not be grouped together. So, it is better to
make applications aware of this when deciding with key to use.
If this is not possible, since AK 2.4 you can take advantage of the sticky partitioner
(KIP-480). This partitioner will “stick” to a partition until a full batch if full making a
better use of batching.

19.
What about the number of clients?
More clients generally mean more load for the Brokers, even if the throughput
remains, there are going to be more metadata requests and connections to be
handled
More clients will have an impact on tail latency, more clients will increase the
number of produce and fetch requests send to a Kafka Broker at a time

20.
Moar partitions, please?

21.
Brought to you by
Thank you!
pere@confluent.io
@purbon