RFR: 7164841: Improvements to the GC log file rotation

[Bernd Eckenfels]

Hello,

no matter what you decide (for example configurable pattern like J9 is  
doing it) please add enough header informatiomn to the logfile that it  
answers common gc diagnostic questions (version, command line settings,  
ram/swap size) and the start wallclock of the segment (for calculating  
abolute times without using the datestamp option).

Greetings
Bernd