[HADOOP-3201] namenode should be able to retrieve block metadata from a datanode

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Duplicate
• Assignee: Tsz-wo Sze
• Reporter: Dhruba Borthakur
• Created: 07/Apr/08 18:13
• Updated: 08/Jul/09 16:43
• Resolved: 21/May/08 23:45

Description

The Append design (HADOOP-1700) requires that the namenode be able to contact the datanode when a lease expires.

When a lease expires, the namenode has to fix up the size of the last block of the file that was being written to. The namenode contacts the datanodes, retrieves the block generation stamp and the length of the lastblock of all known replicas, determines which replicas are good and which one are to be deleted, stamps the winning replicas with a new generation stamp and deletes losing replicas. Once this process is complete, the namenode can allow a new writer to append to this file. Details of this design are in HADOOP-1700.

A few options available to us:

1. The namenode sends the request as a response to the next heartbeat RPC from the datanode. This methodology is currently used for requesting block reports from datanodes.

2. The datanode has an RPC server. A pool of threads in the namenode can be used to make RPCs to the datanodes.

Issue Links

• blocks: HADOOP-1700 Append to files in HDFS
• is blocked by: HADOOP-3254 FSNamesystem.gotHeartbeat(..., Object[] xferResults, Object[] deleteList) should not use Object[] as pass-by-reference parameters