Clarify description of "logging.file.max-history"

[lihongmingming]

The max-history is the maximum retention days of the log，not number. so i think it will bring ambiguity

[bclozel]

The default configuration is rotating files when the size limit is reached and this option is about the maximum number of archive files to keep. The default configuration is not doing daily rollovers.

Even if it did, the official logback documentation is about the maximum number of files and doesn't mention how rotation is configured.

Could you explain what lead you to think that there was a mistake in the docs? Maybe you're experiencing a different problem?

[lihongmingming]

I tested it in my environment. If I set max-history = 3, the logback will clear all logs of three days ago.
So I think this is the number of days to save the file, but it does not refer to the number of logs.

[bclozel]

Could you show your logging options? Did you have other logback configuration files?
Did those log files reach the 10Mb limit?

[lihongmingming]

I only configure it in my bootstrap.yml,did'nt have any other configuration files.

logging:
file:
max-history: 3
max-size: 2KB

[bclozel]

Thanks for the info @lihongmingming !
@wilkinsona and I looked into this and it appears that things can be misleading here.

Spring Boot is using Logback's SizeAndTimeBasedRollingPolicy, which means log files are rotated when the time limit has been reached - also, the log files are split to make sure that files don't exceed the maximum size.

In our case, Spring Boot is using the following pattern %d{yyyy-MM-dd}.%i.gz, which infers daily periods.

This means that, for the following configuration, we might get 14 files if the application logs 20MB every 24hours (2x 10MB files per day):

logging.file.max-history=7
logging.file.max-size=10MB

This holds true, unless developers override the default logback configuration provided by Spring Boot.
I think you're right and we should update the configuration description to reflect that.

Closing in favour of #17567

[bclozel]

I'm wondering if we shouldn't add support for total-size-cap Logback property, because currently the total size of archived logs is unbounded. See example in the Logback docs.

[prodingerd]

I'm wondering if we shouldn't add support for total-size-cap Logback property, because currently the total size of archived logs is unbounded. See example in the Logback docs.

Haven't you done this already? See 999780f.

[bclozel]

Right, thanks @prodingerd