Major Description
When client opens a file, it asks DataNode to check the blocks' visible length. If somehow the block is not on the DN, it throws "Cannot append to a non-existent replica" message, which is incorrect, because getReplicaVisibleLength() is called for different use, just not for appending to a block. It should just state "block is not found"
The following stacktrace comes from a CDH5.13, but it looks like the same warning exists in Apache Hadoop trunk.
2018-05-29 09:23:41,966 INFO org.apache.hadoop.ipc.Server: IPC Server handler 2 on 50020, call org.apache.hadoop.hdfs.protocol.ClientDatanodeProtocol.getReplicaVisibleLength from 10.0.0.14:53217 Call#38334117 Retry#0 org.apache.hadoop.hdfs.server.datanode.ReplicaNotFoundException: Cannot append to a non-existent replica BP-725378529-10.236.236.8-1410027444173:13276792346 at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.getReplicaInfo(FsDatasetImpl.java:792) at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.getReplicaVisibleLength(FsDatasetImpl.java:2588) at org.apache.hadoop.hdfs.server.datanode.DataNode.getReplicaVisibleLength(DataNode.java:2756) at org.apache.hadoop.hdfs.protocolPB.ClientDatanodeProtocolServerSideTranslatorPB.getReplicaVisibleLength(ClientDatanodeProtocolServerSideTranslatorPB.java:107) at org.apache.hadoop.hdfs.protocol.proto.ClientDatanodeProtocolProtos$ClientDatanodeProtocolService$2.callBlockingMethod(ClientDatanodeProtocolProtos.java:17873) at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:617) at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:1073) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2217) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2213) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:422) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1917) at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2211)