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jhat

Java Heap Analysis Tool

  • Only available in JDK 8

References

Quickstart

# Analyze dump file
jhat jmap-dump-all-12345.bin

Synopsis

jhat [ options ] <heap-dump-file>

Options

  • -stack false|true Turns off tracking object allocation call stack.
    • If allocation site information is not available in the heap dump, then you have to set this flag to false.
    • The default is true.
  • -refs false|true Turns off tracking of references to objects.
    • Default is true.
    • By default, back pointers, which are objects that point to a specified object such as referrers or incoming references, are calculated for all objects in the heap.
  • -port port-number Sets the port for the jhat HTTP server.
    • Default is 7000.
  • -exclude exclude-file Specifies a file that lists data members that should be excluded from the reachable objects query.
    • For example, if the file lists java.lang.String.value, then, then whenever the list of objects that are reachable from a specific object o are calculated, reference paths that involve java.lang.String.value field are not considered.
  • -baseline exclude-file Specifies a baseline heap dump.
    • Objects in both heap dumps with the same object ID are marked as not being new.
    • Other objects are marked as new.
    • This is useful for comparing two different heap dumps.
  • -debug int Sets the debug level for this tool.
    • A level of 0 means no debug output.
    • Set higher values for more verbose modes.
  • -version Reports the release number and exits
  • -h | -help Displays a help message and exits.
  • -Jflag Passes flag to the Java Virtual Machine on which the jhat command is running.
    • For example, -J-Xmx512m to use a maximum heap size of 512 MB.

Usage

# IntelliJ IDEA
$ jmap -dump:all,format=b,file=jmap-dump-all-581.bin 581
Heap dump file created

$ jhat jmap-dump-all-581.bin
Reading from jmap-dump-all-581.bin...
Dump file created Thu Aug 20 16:47:13 CST 2020
Snapshot read, resolving...
Resolving 4436517 objects...
Chasing references, expect 887 dots.......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
Eliminating duplicate references.......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
Snapshot resolved.
Started HTTP server on port 7000
Server is ready.