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

[David Holmes]

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
>