笔者在搭建好Hadoop HA 高可用集群启动时报如下错误，后面是解决方案。
报错信息：
2018-08-24 11:18:07,475 INFO org.apache.hadoop.hdfs.server.namenode.FSImage: Quota initialization completed in 31 milliseconds
name space=1
storage space=0
storage types=RAM_DISK=0, SSD=0, DISK=0, ARCHIVE=0
2018-08-24 11:18:07,580 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: FSNamesystem write lock held for 5203 ms via
java.lang.Thread.getStackTrace(Thread.java:1559)
org.apache.hadoop.util.StringUtils.getStackTrace(StringUtils.java:950)
org.apache.hadoop.hdfs.server.namenode.FSNamesystemLock.writeUnlock(FSNamesystemLock.java:261)
org.apache.hadoop.hdfs.server.namenode.FSNamesystem.writeUnlock(FSNamesystem.java:1511)
org.apache.hadoop.hdfs.server.namenode.FSNamesystem.loadFSImage(FSNamesystem.java:1014)
org.apache.hadoop.hdfs.server.namenode.FSNamesystem.loadFromDisk(FSNamesystem.java:686)
org.apache.hadoop.hdfs.server.namenode.NameNode.loadNamesystem(NameNode.java:586)
org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:646)
org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:820)
org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:804)
org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1516)
org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1582)
Number of suppressed write-lock reports: 0
Longest write-lock held interval: 5203
2018-08-24 11:18:07,580 WARN org.apache.hadoop.hdfs.server.namenode.FSNamesystem: Encountered exception loading fsimage
java.io.IOException: There appears to be a gap in the edit log. We expected txid 1, but got txid 904.
at org.apache.hadoop.hdfs.server.namenode.MetaRecoveryContext.editLogLoaderPrompt(MetaRecoveryContext.java:94)
at org.apache.hadoop.hdfs.server.namenode.FSEditLogLoader.loadEditRecords(FSEditLogLoader.java:215)
at org.apache.hadoop.hdfs.server.namenode.FSEditLogLoader.loadFSEdits(FSEditLogLoader.java:143)
at org.apache.hadoop.hdfs.server.namenode.FSImage.loadEdits(FSImage.java:898)
at org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSImage(FSImage.java:753)
at org.apache.hadoop.hdfs.server.namenode.FSImage.recoverTransitionRead(FSImage.java:329)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.loadFSImage(FSNamesystem.java:984)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.loadFromDisk(FSNamesystem.java:686)
at org.apache.hadoop.hdfs.server.namenode.NameNode.loadNamesystem(NameNode.java:586)
at org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:646)
at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:820)
at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:804)
at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1516)
at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1582)
2018-08-24 11:18:07,631 INFO org.mortbay.log: Stopped HttpServer2$SelectChannelConnectorWithSafeStartup@Master:50070
2018-08-24 11:18:07,662 WARN org.apache.hadoop.http.HttpServer2: HttpServer Acceptor: isRunning is false. Rechecking.
2018-08-24 11:18:07,671 WARN org.apache.hadoop.http.HttpServer2: HttpServer Acceptor: isRunning is false
2018-08-24 11:18:07,671 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: Stopping NameNode metrics system...
2018-08-24 11:18:07,672 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: NameNode metrics system stopped.
2018-08-24 11:18:07,672 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: NameNode metrics system shutdown complete.
2018-08-24 11:18:07,672 ERROR org.apache.hadoop.hdfs.server.namenode.NameNode: Failed to start namenode.
java.io.IOException: There appears to be a gap in the edit log. We expected txid 1, but got txid 904.
at org.apache.hadoop.hdfs.server.namenode.MetaRecoveryContext.editLogLoaderPrompt(MetaRecoveryContext.java:94)
at org.apache.hadoop.hdfs.server.namenode.FSEditLogLoader.loadEditRecords(FSEditLogLoader.java:215)
at org.apache.hadoop.hdfs.server.namenode.FSEditLogLoader.loadFSEdits(FSEditLogLoader.java:143)
at org.apache.hadoop.hdfs.server.namenode.FSImage.loadEdits(FSImage.java:898)
at org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSImage(FSImage.java:753)
at org.apache.hadoop.hdfs.server.namenode.FSImage.recoverTransitionRead(FSImage.java:329)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.loadFSImage(FSNamesystem.java:984)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.loadFromDisk(FSNamesystem.java:686)
at org.apache.hadoop.hdfs.server.namenode.NameNode.loadNamesystem(NameNode.java:586)
at org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:646)
at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:820)
at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:804)
at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1516)
at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1582)
2018-08-24 11:18:07,674 INFO org.apache.hadoop.util.ExitUtil: Exiting with status 1
2018-08-24 11:18:07,714 INFO org.apache.hadoop.hdfs.server.namenode.NameNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at Master/192.168.234.136
************************************************************/解决方案：
1.stop hadoop所有的服务;
2.重新格式化namenode即可： hadoop根目录下：./bin/fs namenode -format
hdfs namenode -format
scp -r /usr/local/hadoop/tmp hadoop@Slavel:/usr/local/hadoop/
