arthas/tutorials/katacoda/command-vmtool-en/vmtool.md

Use the vmtool command to find the jvm object.

Find string objects in jvm

vmtool --action getInstances --className java.lang.String{{execute T2}}

$ vmtool --action getInstances --className java.lang.String
@String[][
     @String[Sorry, deque too big],
     @String[head=%d tail=%d capacity=%d%n],
     @String[elements=%s%n],
     @String[sun/nio/ch/IOVecWrapper],
     @String[40252e37-8a73-4960-807e-3495addd5b08:1620922383791],
     @String[40252e37-8a73-4960-807e-3495addd5b08:1620922383791],
     @String[sun/nio/ch/AllocatedNativeObject],
     @String[sun/nio/ch/NativeObject],
     @String[sun/nio/ch/IOVecWrapper$Deallocator],
     @String[Java_sun_nio_ch_FileDispatcherImpl_writev0],
]

limit parameter

Through the --limit parameter, you can limit the number of return values to avoid pressure on the JVM when obtaining large data. The default value is 10.

So the above command is actually equivalent to:

vmtool --action getInstances --className java.lang.String --limit 10

If you set --limit to a negative number, all objects are traversed.