有个默认值的：

TimeBasedRollingPolicy源码，默认maxHistory为0

public class TimeBasedRollingPolicy<E> extends RollingPolicyBase implements TriggeringPolicy<E> {
    static final String FNP_NOT_SET = "The FileNamePattern option must be set before using TimeBasedRollingPolicy. ";
    FileNamePattern fileNamePatternWCS;
    private Compressor compressor;
    private RenameUtil renameUtil = new RenameUtil();
    Future<?> compressionFuture;
    Future<?> cleanUpFuture;
    private int maxHistory = 0;
    private FileSize totalSizeCap = new FileSize(0L);
    private ArchiveRemover archiveRemover;
    TimeBasedFileNamingAndTriggeringPolicy<E> timeBasedFileNamingAndTriggeringPolicy;
    boolean cleanHistoryOnStart = false;

maxFileSize默认值为10485760L Bytes

public class SizeBasedTriggeringPolicy<E> extends TriggeringPolicyBase<E> {
    public static final String SEE_SIZE_FORMAT = "http://logback.qos.ch/codes.html#sbtp_size_format";
    public static final long DEFAULT_MAX_FILE_SIZE = 10485760L;
    String maxFileSizeAsString = Long.toString(10485760L);
    FileSize maxFileSize;
    InvocationGate invocationGate = new DefaultInvocationGate();