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Creating Thread and Heap Dumps

When you are experiencing issues with your Liferay service’s performance, you may need to take thread or heap dumps to help you or Liferay Cloud Support optimize your instance or troubleshoot problems.

Follow these steps to generate thread or heap dumps for troubleshooting:

Choose a script to generate the dumps
Run the script from the Liferay service shell
Download the dumps via the CLI tool
Delete the dumps when you are done

The next section provides example scripts that you can run to generate thread or heap dumps for a Liferay Cloud environment.

Choose a Script to Generate the Dumps

Whether you are generating thread or heap dumps, you can run a script through the Liferay service’s shell to make them available to download via backups.

Thread Dump Creation Script

Thread dumps help you to understand what processes are taking place in your Liferay Cloud environment. Having multiple sets of thread dumps gives a more useful view of whether problematic patterns may exist in your Liferay instance.

You can use this script to generate thread dumps for your Liferay instance in any Liferay Cloud environment:

#!/bin/bash

TARGET_THREAD_DUMP_FOLDER=${TARGET_THREAD_DUMP_FOLDER:-/mnt/persistent-storage/thread_dumps}

mkdir -p "${TARGET_THREAD_DUMP_FOLDER}"

take_thread_dump() {
    mkdir -p "${TARGET_THREAD_DUMP_FOLDER}/${1}"

    local pid=$(jps | grep -v Jps | awk '{print $1}')

    echo "[Liferay Cloud] jstack ${pid} > ${TARGET_THREAD_DUMP_FOLDER}/${1}/threaddump${2}.txt"

    jstack ${pid} > ${TARGET_THREAD_DUMP_FOLDER}/${1}/threaddump${2}.txt
}

take_thread_group() {
    local time=$(date +'%H%M%S')

    echo "[Liferay Cloud] Taking thread dumps with timestamp ${time}"

    for num in 1 2 3 4 5 6
    do
        take_thread_dump $time $num
        sleep 10
    done
}

main() {
    for num in 1 2 3 4
    do
        take_thread_group
        sleep 60
    done

    echo "[Liferay Cloud] Thread dumps generated"
}

echo "[Liferay Cloud] Take thread dumps"
main

This script creates a new folder in your Liferay service’s persistent storage folder (named thread_dumps/ by default), and then it creates multiple timestamped subfolders that each contain a set of thread dumps. By default, it creates four subfolders with timestamps about 60 seconds apart, and fills each subfolder with six thread dumps about 10 seconds apart. Thread dumps are created with the jstack utility.

You can make multiple edits to alter this behavior:

You can change the name of the directory that thread dumps are saved to by changing thread_dumps/ at the end of the path on the first line. However, you must keep the folder inside the /mnt/persistent-storage/ directory for it to be accessible via the CLI tool.
You can change the number of iterations in the main function’s loop to change the number of sets created. You can make the same change in the take_thread_group function to change the number of thread dumps per set.
You can change the period of the sleep command (in seconds) in the main function to change the frequency of each set being created. You can make the same change in the take_thread_group function to change the frequency of thread dumps within each set.

Heap Dump Creation Script

Heap dumps help you to understand what data is consuming RAM in your Liferay instance. If you must troubleshoot your instance’s memory allocation, then you may need to take multiple heap dumps at different, key times to determine if there is an issue.

You can use this script to generate a heap dump for your Liferay instance in any Liferay Cloud environment:

#!/bin/bash

TARGET_HEAP_DUMP_FOLDER=${TARGET_HEAP_DUMP_FOLDER:-/mnt/persistent-storage/heap_dumps}

mkdir -p "${TARGET_HEAP_DUMP_FOLDER}"

take_heap_dump() {
    mkdir -p "${TARGET_HEAP_DUMP_FOLDER}/${1}"

    echo "[Liferay Cloud] Taking heap dump with timestamp ${1}"

    local pid=$(jps | grep -v Jps | awk '{print $1}')

    echo "[Liferay Cloud] jmap -dump:format=b,file=heapdump.txt ${pid}"

    jmap -dump:format=b,file=heapdump.txt ${pid}

    mv heapdump.txt ${TARGET_HEAP_DUMP_FOLDER}/${1}/heapdump.txt
}

main() {
    local time=$(date +'%H%M%S')

    take_heap_dump $time

    echo "[Liferay Cloud] Heap dump generated"
}

main

This script creates a new folder in your Liferay service’s persistent storage folder (named heap_dumps/ by default), and then it creates a timestamped subfolder that contains a single, new heap dump. The heap dump is created with the jmap utility.

You can change the name of the directory that thread dumps are saved to by changing heap_dumps/ at the end of the path on the first line. However, you must keep the folder inside the /mnt/persistent-storage/ folder for it to be accessible via the CLI tool.

Run the Script from the Liferay Service Shell

Once you have a script to use, you must deploy it and run it from the Liferay service’s shell in the Liferay Cloud console.

Save the Script to Your Project Repository

First, save your chosen script into a directory that you can deploy to your Liferay instance’s $LIFERAY_HOME folder.

Create a new folder for manual scripts in your project repository’s Liferay configurations, such as liferay/configs/[ENV]/diagnostics/. Creating the folder in the appropriate liferay/configs/[ENV]/ directory ensures that the folder contents appear in your Liferay instance’s $LIFERAY_HOME once it is deployed.
```
cd liferay/configs/common/
```
```
mkdir diagnostics/
```
Create a generate_thread_dumps.sh or generate_heap_dump.sh file in your project repository’s Liferay configurations, in a new folder for manual scripts (such as liferay/configs/[ENV]/diagnostics/).
```
touch my_script_name.sh
```
Save the desired script’s contents into the new file.

Deploy and Run the Script

Once you have the script saved into a subfolder in liferay/configs/[ENV]/, you must deploy the script and run it from the shell on the Liferay Cloud console.

Follow the steps outlined in Updating Services in Liferay PaaS to deploy the script to the appropriate environment.
In the Liferay Cloud console, navigate to the Liferay service page in the appropriate environment.
Click the Shell tab.

The script you deployed to this environment is in the file system accessible through this shell.
In the shell, navigate to the folder you created and deployed the script to.
```
cd diagnostics/
```
Ensure that you have permission to execute the script you deployed.
```
chmod +x ./generate_thread_dumps.sh
```
Run the script.
```
./generate_thread_dumps.sh
```
Wait until the script completes to ensure that you have the appropriate number of thread dumps. A confirmation message appears when the script has finished creating thread or heap dumps.
```
[Liferay Cloud] Thread dumps generated
```
Note

The heap dump script provided in this section only generates one heap dump. If you need multiple heap dumps to analyze memory usage at different times, then you must run the script again at those times.

When the script has finished running, the thread or heap dump(s) are saved into timestamped subfolders available within /mnt/persistent-storage/. Next, you must download the dumps via the CLI tool to retrieve them locally.

Download the Dumps via the CLI Tool

Obtain the thread or heap dump(s) by downloading them with the CLI tool’s lcp files download command.

From your command prompt, run the lcp files download command to retrieve the dumps. For example, run this command to retrieve all heap dumps from the heap_dumps/ subfolder to a ~/tmp/ destination folder:
```
lcp files download --prefix heap_dumps --dest ~/data/tmp
```

Follow the tool’s instructions to authenticate (if you aren’t already) and select the environment to download from.

Please select a project from the list below:
#      Project                              Status
1      myproject-prd                        Ready
2      myproject-infra                      Ready
3      myproject-uat                        Ready

? Type a number (#) or project name:

The tool begins downloading the dumps from the folder you specified.

Delete the Dumps When You are Done

The thread and/or heap dumps that you generate may take up significant space in your Liferay service’s persistent storage space, especially if you run the scripts multiple times. Remember to delete the dumps from your environment when you do not need them anymore to avoid wasting memory. Use the Liferay service shell in the Liferay Cloud console to delete the dumps.

For example, run these commands from the Liferay Cloud console to delete one set of thread dumps:

cd mnt/persistent-storage/

rm -r <TIMESTAMPED_FOLDER>/

The scripts provided here save the thread and heap dumps into subfolders with a timestamp that you can use to determine when they were created. You can choose to delete only subfolders with timestamps that are no longer needed for your troubleshooting.

Capability:

Cloud

Resource Type:

Official Documentation

Feature:

Cloud Platform Administration

Deployment Approach:

Liferay PaaS