This assumes you have enabled verbose garbage collection. IBMs Garbage Collection and Memory Visualizer can be used to analyze the garbage collection logs (native_stderr.log, native_stdout.log).
In the Garbage Collection and Memory Visualizer tool, select File > Load File. Select the native_stderr.log or native_stdout.log file you will like to analyze. After the log has been parsed, you will be on the Line plot tab and a graph displaying the garbage collection cycles will be displayed. If No data parsed from sources is displayed, this means the log file being loaded is not a valid log file.
At the bottom of the GUI, select the Report tab. This will display tuning recommendations (recommendations is the key word here - the recommendations require contemplation to conclude if the recommendation makes sense) and a summary.
Following are the steps for known recommendations.
It is usually a good idea to compare at least a few of the log's, to see if the tuning recommendations in each log are similar or different. And, it is a best practise to rotate the native_stderr.log and native_stdout.log.