Strategy of SizeAndTimeBaseRollingPolicy

[RicksonLo]

Hello all,

I have the following appender defined in a springboot RestfulAPI web service:

${HOME_LOG}/LogFile.log

    <rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
        <fileNamePattern>${HOME_LOG}/Log/LogFile-%d{yyyy-MM-dd}.%i.log</fileNamePattern>
        <maxFileSize>100MB</maxFileSize>
        <maxHistory>30</maxHistory>
        <totalSizeCap>10GB</totalSizeCap>
    </rollingPolicy>
    
    <encoder>
        <pattern>%d{dd-MM-yyyy HH:mm:ss.SSS} %-4relative [%thread] %-5level %logger{30} - %msg%n</pattern>
    </encoder>
</appender>

Logback version 1.2.3

The web service is running 24x7 and its confident that logs event occurs every day.
Now this is the questions:
On 1 Feb 2024 the service has been offline. the log folder contained logs files from 2 Jan to 31 Jan, which is 30 days-worth of files.
On 1 Apr 2024 the service has been bring online and run up till now. The strange thing is, if I check today (6 Jun 2024) the files of 1 Apr 2024 to 6 May 2024 has been deleted, but the log files before 1 Feb 2024 are left behind.
The log files of 7 May 2024 to 6 Jun 2024 are all here (30 days-worth)

I am confused why the logs before 1 Feb 2024 not being deleted and want to seek some guidance.

---

[Update]
After testing, the deletion of log files seems to depend to a hidden value of {period} which appears to be 30 days.
Under my setting, Log files older than {maxHistory} + {hidden value} days will not be deleted.
eg.
When maxHistory is set to 3, Log files older than 3+30 days from todays are not deleted.
Change maxHistory to 90, then the range will become 90+30 days.

Since there are no visible configuration found in the document to mention about this,
I assume it cannot be fixed by merely change the setting.
For now, I will just close the discussion as unresolved.