11. Find out the distribution of JVM objects

Jstat You can see that JVM Health of , and jstat –gc You can find out JVM GC Relevant status . and jmap、jhat Use it with , It can help us observe JVM Distribution of objects in .

Jmap –heap PID:

This command can print the summary information of a heap , Including the GC Algorithm 、 Heap configuration information 、 Usage information of each memory area ：

Jmap –histo PID:

It will be arranged in descending order according to the memory space occupied by various objects , Put the object that occupies the most memory on the top . So if you just want to briefly understand the current jvm Memory usage of objects in , Just use it directly jmap –histo Command is enough , You can quickly know which object in the current memory occupies a lot of memory space .

Jmap –dump:live,format=b,file=dump.hprof PID:

This command will generate a... In the current directory dump.hprof file , This is a binary format , You can't open it directly , He took this moment JVM The snapshot of all objects in the heap memory is put into the file , For subsequent analysis .

Jhat –port 7000 dump.hprof：

Dump.hprof That is, above hmap Exported files , Use jhat This file can be analyzed .Jhat Built in web The server , Support the graphical analysis of heap dump snapshots through the browser , Specified here http The port number is 7000 port , Just use the browser to access the location of this machine 7000 port , You can graphically analyze the object distribution of heap memory .