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

[Kevin Walls]

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.org/pipermail/hotspot-runtime-dev/attachments/20250129/2ff46652/attachment-0001.htm>