How come Log4J double the size of log file?

问题

My spring application running Log4j through common-logging and slf4j-log4j12 In the following setting

log4j.appender.ROL=org.apache.log4j.RollingFileAppender
log4j.appender.ROL.Encoding=Unicode
log4j.appender.ROL.File=E:\\I_Told_Ya.log
log4j.appender.ROL.MaxFileSize=100000
log4j.appender.ROL.MaxBackupIndex=10
log4j.appender.ROL.layout=org.apache.log4j.PatternLayout
log4j.appender.ROL.layout.ConversionPattern=%d -- %p -- %c -- %m%n

When I set

MaxFileSize=10000000

each log file grows until 19,488kb

When I set

MaxFileSize=10000000

each log file grows until 196kb

When I set

MaxFileSize=10Mb

each log file grows until 20,000kb

Log4J always double the log size from my setting

So what is going on?

these are my dependencies

    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.17</version>
    </dependency>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>apache-log4j-extras</artifactId>
        <version>1.2.17</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>${slf4j.version}</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>jcl-over-slf4j</artifactId>
        <version>${slf4j.version}</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-log4j12</artifactId>
        <version>${slf4j.version}</version>
    </dependency>

来源：https://stackoverflow.com/questions/21841549/how-come-log4j-double-the-size-of-log-file