[HDFS-630] In DFSOutputStream.nextBlockOutputStream(), the client can exclude specific datanodes when locating the next block.

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.20-append
• Fix Version/s: 0.20-append, 0.20.205.0, 0.21.0
• Component/s: hdfs-client, namenode
• Hadoop Flags: Incompatible change, Reviewed
• Assignee: Cosmin Lehene
• Reporter: Ruyue Ma
• Created: 18/Sep/09 07:05
• Updated: 02/Sep/11 21:42
• Resolved: 26/Jan/10 06:21

Description

created from hdfs-200.

If during a write, the dfsclient sees that a block replica location for a newly allocated block is not-connectable, it re-requests the NN to get a fresh set of replica locations of the block. It tries this dfs.client.block.write.retries times (default 3), sleeping 6 seconds between each retry ( see DFSClient.nextBlockOutputStream).

This setting works well when you have a reasonable size cluster; if u have few datanodes in the cluster, every retry maybe pick the dead-datanode and the above logic bails out.

Our solution: when getting block location from namenode, we give nn the excluded datanodes. The list of dead datanodes is only for one block allocation.

Issue Links

• blocks: HBASE-1876 DroppedSnapshotException when flushing memstore after a datanode dies
• is related to: HDFS-200 In HDFS, sync() not yet guarantees data available to the new readers