Clarification on Time-Based Rollover Without Log Events in Logback

[Dushyant-GitHub]

Hi Team,

We are using Logback with a TimeBasedRollingPolicy configured to roll logs on a monthly basis. We've noticed that the rollover to a new log file does not occur automatically when the new month starts -- it only happens after a new log entry is written. This behavior appears consistent even if the configured rollover time (e.g., the 1st of the month) has already passed.

We would like to confirm:

1. Is it expected behavior that Logback only performs time-based rollover when a log event is triggered?

2. If so, is there a recommended way to proactively trigger or force a rollover at the time boundary?

3. Are there any APIs or hooks we can use to check the rollover condition and initiate it manually without writing a log event?

Any guidance or best practices on how to handle this scenario would be greatly appreciated, especially in systems where logging may be quiet for long periods but we still want timely log archival.

[ceki]

@Dushyant-GitHub here is a quote from the documentation of TimeBasedRollingPolicy:

For various technical reasons, rollovers are not clock-driven but depend on the arrival of logging events. For example, on 8th of March 2002, assuming the fileNamePattern is set to yyyy-MM-dd (daily rollover), the arrival of the first event after midnight will trigger a rollover. If there are no logging events during, say 23 minutes and 47 seconds after midnight, then rollover will actually occur at 00:23'47 AM on March 9th and not at 0:00 AM. Thus, depending on the arrival rate of events, rollovers might be triggered with some latency. However, regardless of the delay, the rollover algorithm is known to be correct, in the sense that all logging events generated during a certain period will be output in the correct file delimiting that period.

1 Is it expected behavior that Logback only performs time-based rollover when a log event is triggered?

Yes, the expected behavior that is to perform rollover when a log event arrives after the time boundary is crossed.

2. If so, is there a recommended way to proactively trigger or force a rollover at the time boundary?

I suggest to trigger events when the time boundary is crossed.

3. Are there any APIs or hooks we can use to check the rollover condition and initiate it manually without writing a log event?

I am afraid there is no such API.