Update for OpenJ9 instructions. (#1334)

* Update for OpenJ9 instructions.

Signed-off-by: Matt Nelson <[email protected]>

* fix lint

Signed-off-by: Matt Nelson <[email protected]>

* more lint/spelling.

Signed-off-by: Matt Nelson <[email protected]>

* edit pr

Signed-off-by: Alexandra Tran <[email protected]>

---------

Signed-off-by: Matt Nelson <[email protected]>
Signed-off-by: Alexandra Tran <[email protected]>
Co-authored-by: Alexandra Tran <[email protected]>
Co-authored-by: Alexandra Tran Carrillo <[email protected]>

Author: 3 people

docs/public-networks/get-started/system-requirements.md

@@ -14,6 +14,90 @@ Grafana provides a [sample dashboard](https://grafana.com/grafana/dashboards/102
     CPU requirements are highest when syncing to the network and typically reduce after the node is
     synchronized to the chain head.
 
+## Java distribution and installation
+
+Besu requires an installation of Java 17+ to run.
+We currently recommend two Java distributions, [OpenJDK 17](https://jdk.java.net/17/)
+and [OpenJ9](https://www.eclipse.org/openj9/), though you can experiment based on your needs.
+
+OpenJDK is the default for many Java users and is balanced in performance and garbage collection.
+OpenJ9 consumes less memory and system resources, but can have worse performance on some setups.
+
+If you have more than 32GB RAM (for Besu and your [consensus client](../concepts/the-merge.md)), use OpenJDK.
+If you have less RAM:
+
+* If you're on Linux (or Unix-based) and your CPU is x86-64 bit architecture (like Intel), use OpenJ9.
+* If you're on ARM-64 CPU architecture (Mac M-series, Raspberry Pi), use OpenJDK.
+
+If you have OpenJDK installed or need a fresh installation of OpenJ9, you can pick up the OpenJ9
+docker image, or install the OpenJ9 JDK using the following steps:
+
+1. Get the [binaries](https://github.com/ibmruntimes/semeru17-binaries/releases) corresponding to
+    your OS architecture.
+    For example:
+
+    ```bash
+    wget https://github.com/ibmruntimes/semeru17-binaries/releases/download/jdk-17.0.5%2B8_openj9-0.35.0/ibm-semeru-open-jdk_x64_linux_17.0.5_8_openj9-0.35.0.tar.gz
+    ```
+
+2. Uncompress the binaries:
+
+    === "Command"
+
+        ```bash
+        tar -xvf YOUR_J9_IMAGE.tar.gz
+        ```
+
+    === "Example"
+
+        ```bash
+        tar -xvf ibm-semeru-open-jdk_x64_linux_17.0.5_8_openj9-0.35.0.tar.gz
+        ```
+
+3. Move the binaries to `bin` directory:
+
+    === "Command"
+
+        ```bash
+        sudo cp -r YOUR_IMAGE/ /usr/bin/
+        ```
+
+    === "Example"
+
+        ```bash
+        sudo cp -r jdk-17.0.5+8/ /usr/bin/
+        ```
+
+4. Specify OpenJ9 for Java on your machine:
+
+    === "Command"
+
+        ```bash
+        sudo update-alternatives --install "/usr/bin/java" "java" "/usr/bin/YOUR_IMAGE" 1
+        sudo update-alternatives --config java (and choose OpenJ9)
+        ```
+
+    === "Example"
+
+        ```bash
+        sudo update-alternatives --install "/usr/bin/java" "java" "/usr/bin/jdk-17.0.5+8/bin/java"
+        ```
+
+    Change your `JAVA_HOME` to OpenJ9 (if using the JDK implementation), where `jdk-install-dir` is
+    the installation location you specified:
+
+    === "Command"
+
+        ```bash
+        export JAVA_HOME=jdk-install-dir`
+        ```
+
+    === "Example"
+
+        ```bash
+        export JAVA_HOME=/usr/bin/jdk-17.0.5+8
+        ```
+
 ## Java Virtual Machine size
 
 For Mainnet and testnets, the minimum [Java Virtual Machine (JVM) memory requirement is 8 GB](../how-to/configure-jvm/manage-memory.md).