Heapdumps produce phd format files by default.
Using Heapdump provides more information about Heapdumps. The following example shows the production of a Heapdump. In this case, both a phd and a classic (.txt) Heapdump have been requested by the use of the opts= option.
java -Xgcpolicy:metronome -Xdump:heap:events=vmstop,opts=PHD+CLASSIC -version JVMDUMP006I Processing dump event "vmstop", detail "#00000000" - please wait. JVMDUMP007I JVM Requesting Heap dump using '/home/user/heapdump.20090602.095239.164050.0001.phd' JVMDUMP010I Heap dump written to /home/user/heapdump.20090602.095239.164050.0001.phd JVMDUMP007I JVM Requesting Heap dump using '/home/user/heapdump.20090602.095239.164050.0001.txt' JVMDUMP010I Heap dump written to /home/user/heapdump.20090602.095239.164050.0001.txt JVMDUMP013I Processed dump event "vmstop", detail "#00000000".
See Using Heapdump for more information about analyzing a Heapdump.