JDK 6 poor performance with ipv6 address lookup with debug flag
-Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=6666

Test case attached for both ipv4 and ipv6 (with and without debug flag):
 testV4.bash/testV4-nodebug.bash testV4.jar testV4.java

 testV6.bash/testV6-nodebug.bash testV6.jar testV6.java
 
Minimal peformance difference is seen with and without the debug flag with ipv4.
However, with ipv6, the performance difference between the run with the debug flag vs. witout the debug flag is significant -

test with 6u18 (time results in ms)

{tester}62: ./testV6.bash
Listening for transport dt_socket at address: 6666
Time to do 100 000 getByName=52547

{tester}63: ./testV6-nodebug.bash
Time to do 100 000 getByName=4334


test with 6u21-b07 (time results in ms)

{tester}80: ./testV4-nodebug.bash
Time to do 100 000 getByName=4035
Printing V4 address = /1.1.1.0

{tester}81: ./testV4.bash
Listening for transport dt_socket at address: 6666
Time to do 100 000 getByName=4272
Printing V4 address = /1.1.1.0

{tester}82: ./testV6.bash
Listening for transport dt_socket at address: 6666
Time to do 100 000 getByName=16046

{tester}83: ./testV6-nodebug.bash
Time to do 100 000 getByName=5957