@Alexy
MaxHistory is relative to timedBased Policy date pattern:
in the example shown in this thread you mentioned:
https://mkyong.com/logging/logback-xml-example/
The full rollingPolicy example is:
<rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
<fileNamePattern>logs/archived/app.%d{yyyy-MM-dd}.%i.log.gz</fileNamePattern>
<!-- each archived file, size max 10MB -->
<maxFileSize>10MB</maxFileSize>
<!-- total size of all archive files, if total size > 20GB, it will delete old archived file -->
<totalSizeCap>20GB</totalSizeCap>
<!-- 60 days to keep -->
<maxHistory>60</maxHistory>
</rollingPolicy>
Within the fileNamePattern we see the configured date pattern "%d{yyyy-MM-dd}" which is based on days. So, maxHistory of 60 means in this specific example to retain "60" days.
Now if that date pattern instead was "%d{yyyy-MM-dd_HH}" which is based on hours instead, the same maxHistory=60 would now mean 60 hours of logs. But since this policy also archives on size, the fileNamePattern also includes "%i" which roles the log incrementally each time it reaches the configured maxFileSize= 10MB. So it will keep 60 days of logs; however, each of those 60 days could have 1 too many rolled logs depending on how much logging is output.
app.2024-01-18.1.log.gz
app.2024-01-18.2.log.gz
app.2024-01-18.3.log.gz
app.2024-01-18.4.log.gz
app.2024-01-18.5.log.gz
...
So if your application decides to unexpectedly start producing large amounts of log output, you could quickly consume all your disk space with incremental logs. This is where the TotalSizeCap setting comes into the picture. It's job is to say regardless of number of logs you want to keep (60 days in this specific configuration example), start deleting old archives when total log archives exceeds this configured size cap.
maxHistory is relative to the configured date pattern and is always days.
So comment in above exact example is correct. it is not about number of log files and since pattern is based in days, it is correct.
A better generic comment is:
<!-- Control the maximum number of log archive files kept and asynchronously delete older files -->
since it makes no specific relative to the dat pattern being used. It simply states that the maxHistory value correlates to number of log archives that are retained. What that equates (minutes, hours, days, etc) to depends on the user defined data pattern.
I modified the example in the article you liked that I created with above comment instead of days even though I called it out later in my article for clarity.
In my opinion, TotalSizeCap is something you should use anytime you use the SizeAndTimeBasedRollingPolicy. That is because maxHistory setting does not take into account the incrementally (%i) created log files. So using above example where it is creating daily logs (%d{yyyy-MM-dd}) the maxHistory= 60 says to keep 60 days of logs.
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Thank you,
Matt
