Apache Druid is written in Java and requires a Java runtime. This page provides details about obtaining and configuring a Java runtime for Druid.
Selecting a Java runtime
Druid fully supports Java 8u92+, Java 11, and Java 17. The project team recommends Java 17.
The project team recommends using an OpenJDK-based Java distribution. There are many free and actively-supported distributions available, including Amazon Corretto, Azul Zulu, and Eclipse Temurin. The project team does not recommend any specific distribution over any other.
Druid relies on the environment variables
DRUID_JAVA_HOME to find Java on the machine. You can set
DRUID_JAVA_HOME if there is more than one instance of Java. To verify Java requirements for your environment, run the
In general, the project team recommends using the G1 collector with default settings. This is the default collector in
Java 11 and 17. To enable G1 on Java 8, use
-XX:+UseG1GC. There is no harm in explicitly specifying this on Java 11
or 17 as well.
Garbage collector selection and tuning is a form of sport in the Java community. There may be situations where adjusting garbage collection configuration improves or worsens performance. The project team's guidance is that most people do not need to stray away from G1 with default settings.
Java 9 and beyond (including Java 11 and 17) include the capability for
strong encapsulation of internal JDK APIs. Druid
uses certain internal JDK APIs, which must be added to
--add-opens on the Java command line.
On Java 11, if these parameters are not included, you will see warnings like the following:
WARNING: An illegal reflective access operation has occurred
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
On Java 17, if these parameters are not included, you will see errors on startup like the following:
Exception in thread "main" java.lang.ExceptionInInitializerError
Druid's out-of-box configuration adds these parameters transparently when you use the bundled
similar commands. In this case, there is nothing special you need to do to run successfully on Java 11 or 17. However,
if you have customized your Druid service launching system, you will need to ensure the required Java parameters are
added. There are many ways of doing this. Choose the one that works best for you.
The simplest approach: use Druid's bundled
bin/start-druidscript to launch Druid.
If you launch Druid using
bin/supervise -c <config>, ensure your config file uses
bin/run-druid. This script uses
bin/run-javainternally, and automatically adds the proper flags.
If you launch Druid using a
bin/run-java. Druid's bundled
If you launch Druid without using its bundled scripts, ensure the following parameters are added to your Java command line: