1.Trace trace parameters
1.1 -verbose:gc
-XX:+printGC
Can print brief information about GC
[GC 4790K->374K(15872K), 0.0001606 secs]
[GC 4790K->374K(15872K), 0.0001474 secs]
[GC 4790K->374K(15872K), 0.0001563 secs]
[GC 4790K->374K(15872K), 0.0001682 secs]
1.2-XX:+PrintGCDetails
print GC details
-XX:+PrintGCTimeStamps
Print the timestamp when the CG occurred
example
[GC[DefNew: 4416K->0K(4928K), 0.0001897 secs] 4790K->374K(15872K), 0.0002232 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
1.3 -XX:+PrintGCDetails output
1.4 -Xloggc:log/gc.log
Specify the location of the GC log to output as a file
Help developers analyze problems
1.5 -XX:+PrintHeapAtGC
After each GC , print heap information
1.6
-XX:+TraceClassLoading
Monitoring class loading
1.7 -XX:+PrintClassHistogram
After pressing Ctrl+Break , print the class information:
Display separately: serial number, number of instances, total size, type
2. Heap allocation parameters
2.1-Xmx –Xms
Specify max heap and min heap
2.2 -XX:+HeapDumpOnOutOfMemoryError
Export heap to file when OOM
-XX:+HeapDumpPath
2.3 -XX:OnOutOfMemoryError
On OOM , execute a script
"-XX:OnOutOfMemoryError=D:/tools/jdk1.7_40/bin/printstack.bat %p“
When the program OOM , a dump of the thread will be generated in D:/a.txt
You can send emails and even restart programs when OOM
Path to export OOM
Summary: Resize Young and Survivor Generations Based on Reality
It is officially recommended that the new generation account for 3/8 of the heap
The surviving generation accounts for 1/10 of the young generation
During OOM , remember to dump the heap to ensure that you can troubleshoot on-site problems
3. Assignment parameters of the permanent area
-XX:PermSize -XX:MaxPermSize
Set the initial space and maximum space of the permanent area
How many types can a system hold, they said