Proposed changes to the GC logging flags

Tony Printezis tony.printezis at
Thu Apr 3 21:22:00 UTC 2008

We're proposing a few small changes (and on significant one) to the way 
the GC logging flags work:

a) When +PrintGCDetails is set, +PrintGCTimeStamps should be set by 
default (currently, it has to be set explicitly; what we've found is 
that it's always more useful to have the time stamps in a GC log when 
analyzing it)
b) When -XXloggc: is set, +PrintGCDetails and +PrintGCTimeStamps are set 
automatically (instead of -verbosegc and +PrintGCTimeStamps) (again, for 
us, it's always more useful to have the more detailed +PrintGCDetails 
output in the log when analyzing it)
c) When -verbosegc, +PrintGCDetails, or -Xloggc: are set, 
+TraceClassUnloading is _not_ automatically set, as it is now (it 
polutes the output a bit during Full GCs)

Notice that, for the above, you'll still be able to get the old behavior 
by setting / unsetting some flags; we're just trying to set more 
sensible defaults.

The more significant proposal:

d) Eliminate the -verbosegc format in favor of the (more detailed and 
more useful, though less concise) +PrintGCDetails format. Do people 
still heavily use and rely on the -verbosegc format in a way that 
migration to the +PrintGCDetails format will be difficult?

Your thoughts and feedback on the above will be appreciated. Thank you,

Tony, HS GC Group

| Tony Printezis, Staff Engineer    | Sun Microsystems Inc.          |
|                                   | MS BUR02-311                   |
| e-mail: tony.printezis at    | 35 Network Drive               |
| office: +1 781 442 0998 (x20998)  | Burlington, MA01803-0902, USA  |
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