Proposed changes to the GC logging flags

Tony Printezis tony.printezis at sun.com
Fri Apr 4 09:40:08 PDT 2008


Hi,

Michael Finocchiaro wrote:
> That is good idea to make PGCTS the default with PGCD and I also agree 
> that the TraceClassUnloading is annoying in a gc log.
Cool, thanks.
> I would propose that you look at HP's JVM GC log format as something 
> far easier to parse than the current format.
So, the issue of what GC log format to actually use is kind of 
orthogonal to what we're proposing here. Basically, we're asking: do 
people want two formats (one: the concise, but very unhelpful on most 
cases, -verbosegc format and second: the more useful and elaborate +PGCD 
format) or would most people be happy if we merge those two? FWIW, yes, 
we are considering changing the +PGCD format so that it is more easily 
parseable.

Tony
> http://docs.hp.com/en/5992-1918/ch01s25.html
>
> or perhaps the jstatd format.
>
> After about 5 or 6 years I can almost eyeball the current file format 
> but a numeric based, space or comma-separated list of the GC cause and 
> the memory space allocations would be a lot easier for post-mortem 
> diagnosis and tuning. And, at least in the HP case, the overhead is 
> very minimal (you get almost the same amount of detail as from 
> -XX:+PrintTenuringDistribution in a single line)...and since there 
> still is not a robust and easy-to-use equivalent of HPjmeter 
> (disclosure - I worked for 10 years for HP) for analyzing the JavaSoft 
> HotSpot JVMs, this would be an improvement.
>
> My 2 cents,
> Fino
>
> On Thu, Apr 3, 2008 at 11:22 PM, Tony Printezis 
> <tony.printezis at sun.com <mailto:tony.printezis at sun.com>> 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
>
>     --
>     ----------------------------------------------------------------------
>     | Tony Printezis, Staff Engineer    | Sun Microsystems Inc.          |
>     |                                   | MS BUR02-311                   |
>     | e-mail: tony.printezis at sun.com <mailto:tony.printezis at sun.com>  
>      | 35 Network Drive               |
>     | office: +1 781 442 0998 (x20998)  | Burlington, MA01803-0902, USA  |
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>
>
> -- 
> Michael Finocchiaro
> michael.finocchiaro at gmail.com <mailto:michael.finocchiaro at gmail.com>
> Mobile Telephone: +33 6 67 90 64 39
> MSN: le_fino at hotmail.com <mailto:le_fino at hotmail.com> 

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


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