HDFS追加文件操作 debug日志，为什么会有这些日志输出？

程序可以正常追加文件，但是会输出如下的log日志。请问是为什么？

2015-07-02 15:40:10.738 [org.apache.hadoop.hdfs.LeaseRenewer] [LeaseRenewer:XMJJ09@masters, clients=[DFSClient_NONMAPREDUCE_-756009281_1], created at java.lang.Throwable: TRACE
at org.apache.hadoop.hdfs.LeaseRenewer.<init>(LeaseRenewer.java:202)
at org.apache.hadoop.hdfs.LeaseRenewer.<init>(LeaseRenewer.java:71)
at org.apache.hadoop.hdfs.LeaseRenewer$Factory.get(LeaseRenewer.java:143)
at org.apache.hadoop.hdfs.LeaseRenewer$Factory.access$100(LeaseRenewer.java:90)
at org.apache.hadoop.hdfs.LeaseRenewer.getInstance(LeaseRenewer.java:80)
at org.apache.hadoop.hdfs.DFSClient.getLeaseRenewer(DFSClient.java:805)
at org.apache.hadoop.hdfs.DFSClient.beginFileLease(DFSClient.java:811)
at org.apache.hadoop.hdfs.DFSClient.append(DFSClient.java:1804)
at org.apache.hadoop.hdfs.DFSClient.append(DFSClient.java:1796)
at org.apache.hadoop.hdfs.DistributedFileSystem$4.doCall(DistributedFileSystem.java:323)
at org.apache.hadoop.hdfs.DistributedFileSystem$4.doCall(DistributedFileSystem.java:319)
at org.apache.hadoop.fs.FileSystemLinkResolver.resolve(FileSystemLinkResolver.java:81)
at org.apache.hadoop.hdfs.DistributedFileSystem.append(DistributedFileSystem.java:319)
at org.apache.hadoop.fs.FileSystem.append(FileSystem.java:1163)
at com.xmgps.xmjj.bayonetimport_hdfs.HdfsImporter.openHdfs(HdfsImporter.java:133)
at com.xmgps.xmjj.bayonetimport_hdfs.HdfsImporter.init(HdfsImporter.java:63)
at com.xmgps.xmjj.bayonetimport_hdfs.HdfsImporter.startServer(HdfsImporter.java:51)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeCustomInitMethod(AbstractAutowireCapableBeanFactory.java:1681)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1620)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1549)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:539)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:475)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:304)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:300)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:195)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:703)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:760)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:482)
at org.springframework.context.support.FileSystemXmlApplicationContext.<init>(FileSystemXmlApplicationContext.java:140)
at org.springframework.context.support.FileSystemXmlApplicationContext.<init>(FileSystemXmlApplicationContext.java:84)
at com.xmgps.xmjj.bayonetimport_hdfs.App.main(App.java:30)
] [DEBUG] - Lease renewer daemon for [] with renew id 1 expired
2015-07-02 15:40:10.738 [org.apache.hadoop.hdfs.LeaseRenewer] [LeaseRenewer:XMJJ09@masters, clients=[DFSClient_NONMAPREDUCE_-756009281_1], created at java.lang.Throwable: TRACE
at org.apache.hadoop.hdfs.LeaseRenewer.<init>(LeaseRenewer.java:202)
at org.apache.hadoop.hdfs.LeaseRenewer.<init>(LeaseRenewer.java:71)
at org.apache.hadoop.hdfs.LeaseRenewer$Factory.get(LeaseRenewer.java:143)
at org.apache.hadoop.hdfs.LeaseRenewer$Factory.access$100(LeaseRenewer.java:90)
at org.apache.hadoop.hdfs.LeaseRenewer.getInstance(LeaseRenewer.java:80)
at org.apache.hadoop.hdfs.DFSClient.getLeaseRenewer(DFSClient.java:805)
at org.apache.hadoop.hdfs.DFSClient.beginFileLease(DFSClient.java:811)
at org.apache.hadoop.hdfs.DFSClient.append(DFSClient.java:1804)
at org.apache.hadoop.hdfs.DFSClient.append(DFSClient.java:1796)
at org.apache.hadoop.hdfs.DistributedFileSystem$4.doCall(DistributedFileSystem.java:323)
at org.apache.hadoop.hdfs.DistributedFileSystem$4.doCall(DistributedFileSystem.java:319)
at org.apache.hadoop.fs.FileSystemLinkResolver.resolve(FileSystemLinkResolver.java:81)
at org.apache.hadoop.hdfs.DistributedFileSystem.append(DistributedFileSystem.java:319)
at org.apache.hadoop.fs.FileSystem.append(FileSystem.java:1163)
at com.xmgps.xmjj.bayonetimport_hdfs.HdfsImporter.openHdfs(HdfsImporter.java:133)
at com.xmgps.xmjj.bayonetimport_hdfs.HdfsImporter.init(HdfsImporter.java:63)
at com.xmgps.xmjj.bayonetimport_hdfs.HdfsImporter.startServer(HdfsImporter.java:51)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeCustomInitMethod(AbstractAutowireCapableBeanFactory.java:1681)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1620)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1549)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:539)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:475)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:304)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:300)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:195)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:703)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:760)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:482)
at org.springframework.context.support.FileSystemXmlApplicationContext.<init>(FileSystemXmlApplicationContext.java:140)
at org.springframework.context.support.FileSystemXmlApplicationContext.<init>(FileSystemXmlApplicationContext.java:84)
at com.xmgps.xmjj.bayonetimport_hdfs.App.main(App.java:30)
] [DEBUG] - Lease renewer daemon for [] with renew id 1 exited