Proposal to change the behavior of the timestamp place holder (%t) in log file paths

[David Holmes]

Adding back serviceability-dev

David

On 30/01/2025 11:55 am, David Holmes wrote:
> Plus one to what Kevin says. The current specified behaviour seems to me 
> to be what would be generally desired. If there is a desire for a 
> different kind of timestamp to be used then a proposal to add that would 
> be more appropriate I think. I seem to recall something fairly recent 
> about expanding the notion of "timestamp" that can be used here.
> 
> David
> 
> On 29/01/2025 7:24 pm, Kevin Walls wrote:
>> Hi,
>>
>> Just checking, but are they sure that's what they want? 8-)
>>
>> This relates to files from unified logging, like java - 
>> Xlog:gc*:file%t.out ...creates:  file2025-01-28_21-43-53.out and - 
>> Xlog:help says, "If the filename contains %p, %t and/or %hn, they will 
>> expand to the JVM's PID, startup timestamp and host name, respectively."
>>
>> (Administratively, I think unified logging is under the runtime group, 
>> cc’d.)
>>
>> Using the JVM start time, across all log files, identifies the set of 
>> files that come from the same process.  They will generally sort 
>> together when viewing a directory.  If a single file gets copied 
>> around, it can still be traced back in its group.   When there are 
>> multiple sets of logs in the same directory, the sets should still 
>> sort together.   I see the filename purpose as to identify the log, or 
>> set of logs.
>>
>> Using a new timestamp for each file, the filenames do not identify the 
>> files as being part of the same run.  They may sort together, but may 
>> not if another log series is in the same directory, and once separated 
>> it's hard to regroup them.
>>
>> Using the pid as well will help, but if we see a lot of low-numbered 
>> PIDs then this won't be unique. (With the current startup timestamp, 
>> you will probably use %p for pid in the file as well, in case JVMs 
>> start at the same moment.)
>>
>> Thanks
>>
>> Kevin
>>
>> *From:*serviceability-dev <serviceability-dev-retn at openjdk.org> *On 
>> Behalf Of *Kemper, William
>> *Sent:* Tuesday, January 28, 2025 7:54 PM
>> *To:* serviceability-dev at openjdk.org
>> *Subject:* Proposal to change the behavior of the timestamp place 
>> holder (%t) in log file paths
>>
>> The timestamp place holder in a log filename currently expands to the 
>> startup time of the JVM. When the log is rotated, the filename 
>> containing this timestamp is suffixed with a file number. My 
>> colleagues had expected the placeholder to be evaluated when the 
>> current log file is rotated. They expected the name of each rotated 
>> file to indicate the time the file was created. I think this 
>> expectation is not unreasonable, so I wanted to discuss the 
>> possibility of changing how/when the timestamp placeholder is 
>> evaluated. If there is any appetite for a change like this, I am 
>> willing to do the work. I would prefer to sort out the details before 
>> coding anything, rather than discussing them in a surprise pull request.
>>
>> Thank you for reading,
>>
>> William
>>
>