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

Jesper Wilhelmsson jesper.wilhelmsson at
Fri May 20 13:05:32 UTC 2011

Looks good!

On 05/16/2011 07:57 PM, Yumin Qi wrote:
> Hi, Ramki, Jesper and all
> Changes has beed made according to previous codereview and discussion. New
> webrev available at:
> In this version, also a few cleanup changes.
> The logic now for rotating gc log file is:
> -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=<num_of_files>
> -XX:GCLogFileSize=<logsize>
> UseGCLogFileRotation must be set, if rotation in on depends on other two flag
> settings: they must be > 0, either of them is 0 will lead rotation not set.
> Added a test case to verify(note it lasts ~5 minutes to check file rotation).
> Thanks
> Yumin
> On 05/06/11 03:50 PM, yumin.qi at wrote:
>> 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.
>> 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
>>> 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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