Fixed Window Rolling Policy

When rolling over, FixedWindowRollingPolicy renames files according to a fixed window algorithm as described below.

The fileNamePattern option represents the file name pattern for the archived (rolled over) log files. This option is required and must include an integer token %i somewhere within the pattern.

Here are the available properties for FixedWindowRollingPolicy

Property Name	Type	Description
`minIndex`	int	This option represents the lower bound for the window's index.
`maxIndex`	int	This option represents the upper bound for the window's index.
`fileNamePattern`	String	This option represents the pattern that will be followed by the FixedWindowRollingPolicy when renaming the log files. It must contain the string %i, which will indicate the position where the value of the current window index will be inserted. For example, using MyLogFile%i.log associated with minimum and maximum values of 1 and 3 will produce archive files named MyLogFile1.log, MyLogFile2.log and MyLogFile3.log. Note that file compression is also specified via this property. For example, `fileNamePattern` set to MyLogFile%i.log.zip means that archived files must be compressed using the zip format; gz format is also supported.

Given that the fixed window rolling policy requires as many file renaming operations as the window size, large window sizes are strongly discouraged. When large values are specified by the user, the current implementation will automatically reduce the window size to 20.

Let us go over a more concrete example of the fixed window rollover policy. Suppose that minIndex is set to 1, maxIndex set to 3, fileNamePattern property set to foo%i.log, and that file property is set to foo.log.

Number of rollovers	Active output target	Archived log files	Description
0	foo.log	-	No rollover has happened yet, logback logs into the initial file.
1	foo.log	foo1.log	First rollover. foo.log is renamed as foo1.log. A new foo.log file is created and becomes the active output target.
2	foo.log	foo1.log, foo2.log	Second rollover. foo1.log is renamed as foo2.log. foo.log is renamed as foo1.log. A new foo.log file is created and becomes the active output target.
3	foo.log	foo1.log, foo2.log, foo3.log	Third rollover. foo2.log is renamed as foo3.log. foo1.log is renamed as foo2.log. foo.log is renamed as foo1.log. A new foo.log file is created and becomes the active output target.
4	foo.log	foo1.log, foo2.log, foo3.log	In this and subsequent rounds, the rollover begins by deleting foo3.log. Other files are renamed by incrementing their index as shown in previous steps. In this and subsequent rollovers, there will be three archive logs and one active log file.

The configuration file below gives an example of configuring RollingFileAppender and FixedWindowRollingPolicy. Note that the File option is mandatory even if it contains some of the same information as conveyed with the fileNamePattern option.

Example: Sample configuration of a RollingFileAppender using a FixedWindowRollingPolicy (logback-examples/src/main/resources/chapters/appenders/conf/logback-RollingFixedWindow.xml)

<configuration>
  <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <file>test.log</file>

    <rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy">
      <fileNamePattern>tests.%i.log.zip</fileNamePattern>
      <minIndex>1</minIndex>
      <maxIndex>3</maxIndex>
    </rollingPolicy>

    <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
      <maxFileSize>5MB</maxFileSize>
    </triggeringPolicy>
    <encoder>
      <pattern>%-4relative [%thread] %-5level %logger{35} - %msg%n</pattern>
    </encoder>
  </appender>

  <root level="DEBUG">
    <appender-ref ref="FILE" />
  </root>
</configuration>

Fixed window rolling policy

Fixed Window Rolling Policy

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