History

Lucas Brutschy fc2e3dfce9 MINOR: Disallow unused local variables (#18963 ) Recently, we found a regression that could have been detected by static analysis, since a local variable wasn't being passed to a method during a refactoring, and was left unused. It was fixed in [`7a749b5`](`7a749b589f`), but almost slipped into 4.0. Unused variables are typically detected by IDEs, but this is insufficient to prevent these kinds of bugs. This change enables unused local variable detection in checkstyle for Kafka. A few notes on the usage: - There are two situations in which people actually want to have a local variable but not use it. First, there are `for (Type ignored: collection)` loops which have to loop `collection.length` number of times, but that do not use `ignored` in the loop body. These are typically still easier to read than a classical `for` loop. Second, some IDEs detect it if a return value of a function such as `File.delete` is not being used. In this case, people sometimes store the result in an unused local variable to make ignoring the return value explicit and to avoid the squiggly lines. - In Java 22, unsued local variables can be omitted by using a single underscore `_`. This is supported by checkstyle. In pre-22 versions, IntelliJ allows such variables to be named `ignored` to suppress the unused local variable warning. This pattern is often (but not consistently) used in the Kafka codebase. This is, however, not supported by checkstyle. Since we cannot switch to Java 22, yet, and we want to use automated detection using checkstyle, we have to resort to prefixing the unused local variables with `@SuppressWarnings("UnusedLocalVariable")`. We have to apply this in 11 cases across the Kafka codebase. While not being pretty, I'd argue it's worth it to prevent bugs like the one fixed in [`7a749b5`](`7a749b589f`). Reviewers: Andrew Schofield <aschofield@confluent.io>, David Arthur <mumrah@gmail.com>, Matthias J. Sax <matthias@confluent.io>, Bruno Cadonna <cadonna@apache.org>, Kirk True <ktrue@confluent.io>		2025-03-10 09:37:35 +01:00
..
bin	KAFKA-18388 test-kraft-server-start.sh should use log4j2.yaml (#18370 )	2025-01-07 04:20:06 +08:00
config	KAFKA-18388 test-kraft-server-start.sh should use log4j2.yaml (#18370 )	2025-01-07 04:20:06 +08:00
src	MINOR: Disallow unused local variables (#18963 )	2025-03-10 09:37:35 +01:00
.gitignore	KAFKA-13429: ignore bin on new modules (#11415 )	2021-11-10 14:36:24 -06:00
README.md	KAFKA-17728 Add missing config `replica-directory-id` to raft README (#17518 )	2024-10-17 11:32:27 +08:00

README.md

KRaft (Kafka Raft)

KRaft (Kafka Raft) is a protocol based on the Raft Consensus Protocol tailored for Apache Kafka.

This is used by Apache Kafka in the KRaft (Kafka Raft Metadata) mode. We also have a standalone test server which can be used for performance testing. We describe the details to set this up below.

Run Single Quorum

bin/test-kraft-server-start.sh --config config/kraft.properties --replica-directory-id b8tRS7h4TJ2Vt43Dp85v2A

Run Multi Node Quorum

Create 3 separate KRaft quorum properties as the following:

cat << EOF >> config/kraft-quorum-1.properties

node.id=1
listeners=PLAINTEXT://localhost:9092
controller.listener.names=PLAINTEXT
controller.quorum.voters=1@localhost:9092,2@localhost:9093,3@localhost:9094
log.dirs=/tmp/kraft-logs-1
EOF

cat << EOF >> config/kraft-quorum-2.properties

node.id=2
listeners=PLAINTEXT://localhost:9093
controller.listener.names=PLAINTEXT
controller.quorum.voters=1@localhost:9092,2@localhost:9093,3@localhost:9094
log.dirs=/tmp/kraft-logs-2
EOF

cat << EOF >> config/kraft-quorum-3.properties

node.id=3
listeners=PLAINTEXT://localhost:9094
controller.listener.names=PLAINTEXT
controller.quorum.voters=1@localhost:9092,2@localhost:9093,3@localhost:9094
log.dirs=/tmp/kraft-logs-3
EOF

Open up 3 separate terminals, and run individual commands:

bin/test-kraft-server-start.sh --config config/kraft-quorum-1.properties --replica-directory-id b8tRS7h4TJ2Vt43Dp85v2A
bin/test-kraft-server-start.sh --config config/kraft-quorum-2.properties --replica-directory-id Nkij_D9XRiYKNb41SiJo7Q
bin/test-kraft-server-start.sh --config config/kraft-quorum-3.properties --replica-directory-id 4-e97nI7eHPYKfEDtW8rtQ

Once a leader is elected, it will begin writing to an internal __raft_performance_test topic with a steady workload of random data. You can control the workload using the --throughput and --record-size arguments passed to test-kraft-server-start.sh.