Request for review: 6941923: RFE: Handling large log files produced by long running Java Applications

yumin.qi at yumin.qi at
Fri May 6 22:50:33 UTC 2011

  Hi, Ramki and all

   This is a new webrev for the changes.

   In this change, a class rotatingFileStream derived from fileStream 
used to handle log rotation. UseGCLogFileRotation is a must for doing gc 
log rotation, and it depends on other two flag setting for the rotation 
really to happen:

   To enable gc log rotation,
   -Xloggc:<filename> -XX:+UseGCLogFileRotation 
-XX:NumberOfGCLogFiles=<num_of_files> -XX:GCLogFileSize=<num_of_size>

   where num_of_files > 0 and num_of_size > 0
   Either one of above is 0 will lead to not having GC log rotation, 
this is the default as no changes.
   For NumberOfGCLogFiles=1, the log file name will be <filename>.0 and 
log output rotation happens in one file. For NumberOfGCLogFiles > 1, 
happens in multiple files.

   filename must be provided or rotation will not set.

   I added another flag, MinGCLogFileSize, this is for test purpose, to 
make the test case can run in a short period to verify the code changes. 
Default value is 32MB, if GCLogFileSize set to less than this number, it 
will be set to MinGCLogFileSize.

   As mentioned, a test case added to verify the result.


On 5/5/2011 9:35 AM, Y. S. Ramakrishna wrote:
> Hi Yumin --
> On 05/05/11 08:38, Yumin Qi wrote:
> ...
>> So, default behavior not changed if GCLogFileSize=0 and 
>> NumberOfGCLogFiles=0.
>> If #file > 0, but GCLogFileSize=0, it is still confused since we use 
>> file.0 and output to it at no limit. The #file seems only make sense 
>> for 1.
> Well, I was using a limit ordinal analogy here. When you reach the
> first limit ordinal, \omega, you will flip to the next file.
> Of course in real life we won't. But it's OK to do what you
> suggest below. It just entails extra args checking, which is fine too.
>> I would like if #file > 0 and GCLogFileSize=0, we still keep current 
>> behavior - no rotation. (GCLogFileSize default is 0, no limit as you 
>> said).
> That's fine too.
>> That is, if rotation stands, UseGCLogRotation ,must be true.
>> 1) If GCLogFileSize is default (0), no rotation; UseGCLogFileRotation 
>> is false
>> 2) If #file is default (0), no rotation.   UseGCLogFileRotation is 
>> false.
> OK; i am sure you will need to straighten this out in the
> CCC spec and spell out the restrictions if any on
> the allowed combinations etc.
>> This is why I need your review here. The rotation only done at STW, 
>> so seems the lock is not necessary here. Remove the locking code, 
>> will put comments to indicating this function only called at 
>> safepoint and add assert at safepoint.
> It's fine to do the locking. I have no objection to the locking;
> my question was why the locking was elided for those two cases.
> It would seem to me that you'd need some way to make sure that
> the stream is not under active use when the rotation occurs,
> and the lock would be a fine way to ensure that the stream is
> never accessed except under protection of the lock. I can see
> that the rotation is done at a STW pause when no mutator is
> running. It turns out today that no daemons run at that time
> either, but it is conceivable that some may in the future
> and have access to or attempt tp access that stream/log.
> We should make the code robust in the face of future such
> evolution, by at least putting in enough controls, and
> the lock would seem to me to be a fine mechanism to do so.
> (After auditing the code to make sure that the handle is
> not accessible outside the lock.)
> -- ramki

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