7090324: gclog rotation via external tool

James Melvin james.melvin at oracle.com
Thu Sep 29 12:15:20 UTC 2011

Hi Yasumasa,

Thanks very much for your OpenJDK contribution! As part of the effort to
port JRockit features to HotSpot, we plan to introduce a consolidated
commandline serviceability tool (jcmd) to potentially replace many of
the existing tools in the bin directory, such as jmap, jstack, jinfo and
others. Over the next few update releases, we plan to add several jcmd
*subcommands* instead to accomplish specific tasks or affect the running
JVM instance. We'd like to use the essence of your contribution in one
of the jcmd subcommands (instead of extending jinfo) to ask the JVM to
begin rotating GC logs. We hope you find this attractive and hope you
will help review and perfect the change.


Jim Melvin
Sr. Engineering Manager

On 9/26/11 6:38 AM, Yasumasa Suenaga wrote:
> (I've changed subject of this email to new RFE.)
> This RFE is enhancement of current gclog implementation.
> So, I'd like to discuss about rotating gclog.
> My customers need gclog rotation which is invoked by external trigger.
> So I've requested this RFE and made a patch.
> In many case on Linux, logfile is rotated by signal (e.g. SIGHUP) .
> The aim of this RFE is to synchronize gclog and the other logs.
> Thanks,
> Yasumasa
> (2011/09/22 20:55), Rainer Jung wrote:
>> On 22.09.2011 13:20, Dmitry Samersoff wrote:
>>> Yasumasa,
>>> On 2011-09-22 04:47, Yasumasa Suenaga wrote:
>>>> If we can think Java on Linux and Solaris only, syslog is best
>>>> solution.
>>>> However, Windows usually doesn't have syslog.
>>>> So, I think that gclog is needed for logging GC stats with platform
>>>> independent in realtime.
>>> Windows has it's own logging API as reach as syslog is or ever better
>>> as well as numerous syslog implementations.
>>> Native windows logging API was completely redesigned for Windows 2008
>>> server and now it allows for developers to send a structured events from
>>> theirs application.
>> AFAIK log rotation for loggc is already implemented though not
>> necessarily yet released. The change discussed here is about supporting
>> an externally generated rotation trigger, e.g. via a signal, instead of
>> only rotating by size or time via a startup parameter.
>> If you want support for syslog or Windows APIs included, it would be
>> best to start a new discussion.
>> A GC log for an application under load might easily produce a block of
>> about 1.5 KB size every few seconds. I seriously doubt, that the need
>> for log file rotation can be argued away by referring to syslog or
>> Windows log API as the correct solution.
>> The messages are not really line formatted, the format can vary a lot
>> (depending on the excat XX switches), the traffic can be quite high and
>> AFAIK the JVM writes it synchronously, so there must be absolutely no
>> risk in writing it out with very little latency. In addition, for
>> analysis, you wouldn't want to look at each event individually, but
>> instead process the whole file through a script or tool, which should
>> not depend on the output specifics of a platform specific log apparatus.
>> Regards,
>> Rainer

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