[HBASE-16212] Many connections to datanode are created when doing a large scan

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Not A Bug
• Affects Version/s: 1.1.2
• Assignee: Unassigned
• Reporter: Zhihua Deng
• Created: 12/Jul/16 03:19
• Updated: 09/Jul/20 01:41
• Resolved: 07/Nov/16 09:29

Description

As described in https://issues.apache.org/jira/browse/HDFS-8659, the datanode is suffering from logging the same repeatedly. Adding log to DFSInputStream, it outputs as follows:

2016-07-10 21:31:42,147 INFO [B.defaultRpcServer.handler=22,queue=1,port=16020] hdfs.DFSClient: DFSClient_NONMAPREDUCE_1984924661_1 seek DatanodeInfoWithStorage[10.130.1.29:50010,DS-086bc494-d862-470c-86e8-9cb7929985c6,DISK] for BP-360285305-10.130.1.11-1444619256876:blk_1109360829_35627143. pos: 111506876, targetPos: 111506843
...
As the pos of this input stream is larger than targetPos(the pos trying to seek), A new connection to the datanode will be created, the older one will be closed as a consequence. When the wrong seeking ops are large, the datanode's block scanner info message is spamming logs, as well as many connections to the same datanode will be created.

hadoop version: 2.7.1