private File getNextChildLogFile() {
    String path = config.getLogFile().getPath();
    int extIndex = path.lastIndexOf('.');
    String ext = "";
    if (extIndex != -1) {
      ext = path.substring(extIndex);
      path = path.substring(0, extIndex);
    }
    path = path + rollingFileHandler.formatId(mainLogId) + rollingFileHandler.formatId(childId)
        + ext;
    childId++;
    File result = new File(path);
    if (result.exists()) {
      // try again until a unique name is found
      return getNextChildLogFile();
    } else {
      return result;
    }
  }
Call when the config changes at runtime.
geode-core/src/main/java/org/apache/geode/internal/logging/ManagerLogWriter.java