jstat is a command-line tool that is included with the Java Development Kit (JDK). It is used to monitor and troubleshoot Java applications by providing information on the performance of the Java virtual machine (JVM) and the Java heap.
jstat can be used to monitor a variety of different metrics, including class loading, memory usage, garbage collection, and just-in-time (JIT) compilation. It can also be used to monitor the performance of individual Java threads.
To use jstat, you must specify the process ID of the Java process you want to monitor, as well as the type of statistics you want to retrieve. You can also specify a sampling interval to control how often the statistics are collected.
Here is an example of using jstat to retrieve class loading statistics for a Java process with a process ID of 1234, with a sampling interval of 1000 milliseconds:
jstat -class 1234 1000
This command will retrieve class loading statistics for the Java process with a process ID of 1234, and print the results to the console every 1000 milliseconds.
jstat provides a number of options for specifying the type of statistics to retrieve. For example, the -gc option can be used to retrieve garbage collection statistics, and the -compiler option can be used to retrieve JIT compilation statistics.
Here is an example of using jstat to retrieve garbage collection statistics for a Java process with a process ID of 1234, with a sampling interval of 1000 milliseconds:
jstat -gc 1234 1000
jstat can be a useful tool for monitoring the performance of a Java application and identifying potential issues. It provides detailed information on the resources being used by the JVM and the Java heap, and can help developers optimize the performance of their applications and resolve problems such as memory leaks or excessive garbage collection.
One potential disadvantage of jstat is that it is a command-line tool, which can make it less user-friendly than graphical tools such as JVisualVM. However, jstat can be more convenient to use in certain situations, such as when you need to monitor a remote Java process or when you want to automate the collection of statistics.
In conclusion, jstat is a powerful and useful tool for monitoring and troubleshooting Java applications. It provides a wealth of information on the performance of the JVM and the Java heap, and can help developers optimize the performance of their applications and identify and fix problems.