Performance tuning in Jenkins - Commands & Configuration

Introduction

Jenkins can slow down when many jobs run or when resources are limited. Performance tuning helps Jenkins run faster and handle more work smoothly.

When Jenkins jobs take too long to start or finish

When the Jenkins server uses too much CPU or memory

When many users access Jenkins at the same time and it becomes slow

When build queues grow and jobs wait too long to run

When Jenkins logs grow too large and slow down the system

Config File - jenkins.xml

jenkins.xml

<?xml version="1.0" encoding="UTF-8"?>
<jenkins>
  <numExecutors>4</numExecutors>
  <quietPeriod>5</quietPeriod>
  <scmCheckoutRetryCount>2</scmCheckoutRetryCount>
  <workspaceDir>${JENKINS_HOME}/workspace/${ITEM_FULL_NAME}</workspaceDir>
  <buildsDir>${JENKINS_HOME}/builds/${ITEM_FULL_NAME}</buildsDir>
  <systemMessage>Jenkins tuned for better performance</systemMessage>
</jenkins>

numExecutors: Number of parallel jobs Jenkins can run.

quietPeriod: Wait time before starting a job to group changes.

scmCheckoutRetryCount: Number of retries for source code checkout to avoid failures.

workspaceDir and buildsDir: Paths to store job data efficiently.

systemMessage: Shows a message on Jenkins dashboard.

Commands

Starts Jenkins with a maximum of 100 HTTP handler threads to handle more simultaneous requests.

Terminal

java -jar jenkins.war --httpPort=8080 --handlerCountMax=100

Expected Output

Running from: /home/jenkins/jenkins.war

INFO: Jenkins is fully up and running

INFO: HTTP connector started on port 8080

INFO: Maximum handler count set to 100

→

--httpPort=8080 - Sets the HTTP port Jenkins listens on

→

--handlerCountMax=100 - Increases max concurrent HTTP handlers for better performance

Runs a Groovy script via Jenkins CLI to enable performance optimizations like disabling unused plugins.

Terminal

jenkins-cli.jar -s http://localhost:8080 groovy = < enable_performance_optimizations.groovy

Expected Output

Performance optimizations enabled successfully

Restarts Jenkins service to apply configuration and performance changes.

Terminal

systemctl restart jenkins

Expected Output

No output (command runs silently)

Checks the status of Jenkins jobs to verify Jenkins is responsive after tuning.

Terminal

curl -s http://localhost:8080/api/json?tree=jobs[name,color] | jq

Expected Output

{

  "jobs": [

    {"name": "build-app", "color": "blue"},

    {"name": "test-app", "color": "red"}

  ]

}

→

-s - Runs curl silently without progress output

Key Concept

If you remember nothing else from performance tuning Jenkins, remember: adjust executors and resource limits to match your workload.

Common Mistakes

Setting numExecutors too high without enough CPU or memory

Jenkins will overload the server causing slowdowns or crashes

Set numExecutors based on available CPU cores and memory capacity

Not restarting Jenkins after changing configuration

Changes will not take effect until Jenkins restarts

Always restart Jenkins service after config changes

Ignoring plugin performance impact

Unused or heavy plugins can slow Jenkins down

Disable or remove plugins that are not needed

Summary

Start Jenkins with increased handler count to handle more requests.

Configure numExecutors and retry counts in jenkins.xml for better job management.

Restart Jenkins to apply changes and verify responsiveness with API calls.