将日志信息改成DEBUG模式，这样就能知道hadoop里RPC里Client的相关交互机制了。
下面是以hadoop dfsadmin -report这个命令作为示例
[hadoop@master bin]$ hadoop dfsadmin -report
Warning: $HADOOP_HOME is deprecated.
12/06/28 14:04:06 DEBUG ipc.Client: The ping interval is5000ms.
12/06/28 14:04:06 DEBUG ipc.Client: Use SIMPLE authentication for protocol ClientProtocol
12/06/28 14:04:06 DEBUG ipc.Client: Connecting to master/10.200.187.77:8020
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop sending #0
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop: starting, having connections 1
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop got value #0
12/06/28 14:04:06 DEBUG ipc.RPC: Call: getProtocolVersion 93
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop sending #1
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop got value #1
12/06/28 14:04:06 DEBUG ipc.RPC: Call: getProtocolVersion 2
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop sending #2
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop got value #2
12/06/28 14:04:06 DEBUG ipc.RPC: Call: getStats 3
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop sending #3
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop got value #3
12/06/28 14:04:06 DEBUG ipc.RPC: Call: setSafeMode 1
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop sending #4
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop got value #4
12/06/28 14:04:06 DEBUG ipc.RPC: Call: distributedUpgradeProgress 2
Configured Capacity: 4346957316096 (3.95 TB)
Present Capacity: 4102886871025 (3.73 TB)
DFS Remaining: 3326354513920 (3.03 TB)
DFS Used: 776532357105 (723.2 GB)
DFS Used%: 18.93%
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop sending #5
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop got value #5
12/06/28 14:04:06 DEBUG ipc.RPC: Call: getStats 0
Under replicated blocks: 645
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop sending #6
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop got value #6
12/06/28 14:04:06 DEBUG ipc.RPC: Call: getStats 1
Blocks with corrupt replicas: 0
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop sending #7
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop got value #7
12/06/28 14:04:06 DEBUG ipc.RPC: Call: getStats 0
Missing blocks: 0
-------------------------------------------------
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop sending #8
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop got value #8
12/06/28 14:04:06 DEBUG ipc.RPC: Call: getDatanodeReport 6
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop sending #9
12/06/28 14:04:06 DEBUG ipc.Client: IPC Client (47) connection to master/10.200.187.77:8020 from hadoop got value #9
12/06/28 14:04:06 DEBUG ipc.RPC: Call: getDatanodeReport 0
Datanodes available: 3 (3 total, 0 dead)
Name: 10.200.187.79:50010
Decommission Status : Normal
Configured Capacity: 1448985772032 (1.32 TB)
DFS Used: 258844090368 (241.07 GB)
Non DFS Used: 83790385152 (78.04 GB)
DFS Remaining: 1106351296512(1.01 TB)
DFS Used%: 17.86%
DFS Remaining%: 76.35%
Last contact: Thu Jun 28 14:04:06 CST 2012
Name: 10.200.187.78:50010
Decommission Status : Normal
Configured Capacity: 1448985772032 (1.32 TB)
DFS Used: 258843840497 (241.07 GB)
Non DFS Used: 79234711567 (73.79 GB)
DFS Remaining: 1110907219968(1.01 TB)
DFS Used%: 17.86%
DFS Remaining%: 76.67%
Last contact: Thu Jun 28 14:04:04 CST 2012
Name: 10.200.187.80:50010
Decommission Status : Normal
Configured Capacity: 1448985772032 (1.32 TB)
DFS Used: 258844426240 (241.07 GB)
Non DFS Used: 81045348352 (75.48 GB)
DFS Remaining: 1109095997440(1.01 TB)
DFS Used%: 17.86%
DFS Remaining%: 76.54%
Last contact: Thu Jun 28 14:04:05 CST 2012