What is jmap's default heapdump format?

Question

We are taking heapdumps and have a question:

jmap -dump:file=heapdump.hprof,format=b

• If you specify format=a it will be usage message in ascii
• If you specify format=b it will be binary

OK great, but what if you don't specify a format at all?

jmap -dump:file=heapdump.hprof

Which one will it pick?

Answer 1

The default is binary data file (hprof). You can just try running the command without specifying the format and with format=b and you will find out yourself that they have the same format.

alessio$ file heapdump.hprof 
heapdump.hprof: data