@Override
    public void shutdown() {
        doCheckpoint();
        if (this.serviceManager != null) {
            this.serviceManager.shutdown();
        }
        if (this.fileManager != null) {
            this.fileManager.shutdown();
        }
        if (this.abortFile != null) {
            this.abortFile.destroy();
        }
        this.checkpointExecutor.shutdown();
    }
DB parent class that invokes fileManager and anager
and wrappers uniform functions such as recover() etc..
@author hzh (642256541@qq.com)
jraft-extension/java-log-storage-impl/src/main/java/com/alipay/sofa/jraft/storage/db/AbstractDB.java