Version v0.42 of Metabase is no longer supported. Check out the docs for the current stable version, Metabase v0.63.
Monitoring via JMX
Diagnosing performance related issues can be a challenge. Luckily the JVM ships with tools that can help diagnose many common issues. Enabling JMX and using a tool like VisualVM can help diagnose issues related to running out of memory, a hung Metabase instance and slow response times. See Monitoring via JMX for more information on setting this up.
Read docs for other versions of Metabase.