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

yumin.qi at oracle.com yumin.qi at oracle.com
Fri May 6 15:50:33 PDT 2011

  Hi, Ramki and all

This is a new webrev for the changes.
http://cr.openjdk.java.net/~minqi/6941923/webrev.04

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.

Thanks
Yumin

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