How does Log4j2 DefaultRolloverStrategy's max attribute really work?

Question

I've configured a RollingRandomAccessFileAppender with only the OnStartupTriggeringPolicy set, but when I set the max attribute of the DefaultRolloverStrategy to some number, the logs keep generating past that amount indefinitely.

Here's my log4j2.xml :

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
        </Console>
        <RollingRandomAccessFile 
            name="RollingRAF" 
            fileName="logs/app.log"
            filePattern="logs/app-%d{dd-MMM-yyyy@HH.mm.ss}.log">
            <PatternLayout>
                <Pattern>%d %p %c{1.} %m%n</Pattern>
            </PatternLayout>
            <Policies>
                <OnStartupTriggeringPolicy />
            </Policies>
            <DefaultRolloverStrategy max="5"/>
        </RollingRandomAccessFile>
    </Appenders>
    <Loggers>
        <Logger name="myLogger" level="warn">
            <AppenderRef ref="RollingRAF"/>
        </Logger>
        <Root level="error">
            <AppenderRef ref="Console"/>
        </Root>
    </Loggers>
</Configuration>

Is it because I don't have an iterator in my name pattern?

Is it because my file name precision is set to seconds?

Is it because I only have the OnStartupTriggeringPolicy set?

Or what's going on here?

My goal here was to set up a rolling configuration that will log the last 5 application runs.

Answer 1

The DefaultRolloverStrategy will use the date pattern specified in the filePattern if a TimeBasedTriggeringPolicy is specified. To use the max attribute, specify a %i pattern in the filePattern, and add <SizeBasedTriggeringPolicy size="20 MB" /> to the rollover policies. (Or some other size of course.)

The value for max in <DefaultRolloverStrategy max="5"/> will then ensure that within the same rollover period (one second for you since you specified a date pattern of %d{dd-MMM-yyyy@HH.mm.ss} ) no more than 5 files will be created when a size-based rollover was triggered.

This is more useful if your rollover window is longer, like rolling over to a new folder every day, and within that folder, ensure that no more than 5 files are created with max size=20 MB.

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Update:

Log4j 2.5 added the ability to configure custom delete actions . Out of the box you can delete files based on age, count or how much disk space they take up (accumulated file size).