Proposed changes to the GC logging flags

Adam Hawthorne adamh at
Fri Apr 4 17:40:18 UTC 2008

We always require customers to enable the -XX:+PrintGCDetails and
PrintGCTimeStamps... making -verbose:gc do this by default would be a
welcome change for us.  The -verbose:gc output is not helpful for us.



On Thu April 3 2008, Tony Printezis wrote:
> 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

Adam Hawthorne
Software Engineer
BASIS International Ltd.
+1.505.345.5232 Phone

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