7.4.3 How to check the usage of memory size of Java heap
Keep tuning the respective memory sizes while measuring the memory usage by actually running the application. In the Application Server, you can output the detailed memory size of each area when GC is executed in the form of extended verbosegc information by specifying the XX:+HitachiVerboseGC option in the usrconf.cfg file and invoking the J2EE server. Tune on the basis of this output.
The main contents that can be output in the form of extended verbosegc information are as follows:
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The date and time GC occurred
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GC type
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GC information#1
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Elapsed time of GC
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Eden information#1
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Survivor information#1
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Tenured information#1
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Metaspace area information#1
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GC factors#2
- #1
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The usage area length and the area size before and after GC are output.
- #2
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Output, when the -XX:+HitachiVerboseGCPrintCause option is specified.
For details about the output examples of extended verbosegc information and how to analyze the factors responsible for Full GC, see 7.10 Analyzing the factors of Full GC using the extended verbosegc information. For details about the options, see -XX:[+|-]HitachiVerboseGC (Option for extended verbosegc information output) in the uCosminexus Application Server Definition Reference Guide.
You can also use the javagc command on the Application Server to trigger Full GC at any time. In this case, you can output the same contents as the extended verbosegc information, by specifying the -v option. For details about the javagc command, see javagc (forcibly perform GC) in the uCosminexus Application Server Command Reference Guide.