Tomcat 8的系统RAM的最大使用率

Question

I have a PC which contains 8 GB RAM and more than 5 GB free RAM. The picture below shows more details.

What's the maximum usage of RAM memory allocated for Tomcat according to the picture and how can I increase this usage limit?

The Operating System is Windows 7 64-bit

Answer 1

According to the image you posted, the current Java maximum heap size has been set to (or has defaulted to) 1819 MB.

The theoretical maximum for your machine will be something in the vicinity of 12 to 14 GB, based on the page file size. (It is difficult to be sure because it depends on what other OS processes, etc are using space in the page file.)

A more practical limit would be around 6GB, based on the current amount of free RAM reported by the OS. (You could go above 6GB, but if you push memory usage beyond the limits of physical RAM, there is a risk that performance will be degraded due to VM thrashing, especially during major garbage collections.)

If want to increase the Tomcat JVM's max heap size beyond what it is currently set to, you need to find the place where Tomcat's JVM command line options are set, and add an -Xmx... option (or modify the existing one).

Refer to the Tomcat documentation for your platform and / or the manual entry for the java command where the JVM heap sizing options are documented.

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On the flipside, 1800 MB should be plenty of space for a typical Tomcat service. And it looks like your JVM is not under memory pressure at the moment. Based on this information, I wouldn't be looking to change the max heap size right now.

Answer 2

From the picture it seems that you are using a Windows 7, 64 bits. To allocate more memory to your tomcat instance you will have to play with the JVM initialisation params.

Example given:

-Xms2G -Xmx6G -XX:PermSize=256m -XX:MaxPermSize=512m

On Windows you might want to add these to your JAVA_OPTS in your bin/catalina.bat

Here is a reading suggestion around the params: http://www.mkyong.com/java/find-out-your-java-heap-memory-size/