[HDFS-1384] NameNode should give client the first node in the pipeline from different rack other than that of excludedNodes list in the same rack.

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Incomplete
• Affects Version/s: 0.20.1, 0.20-append
• Assignee: Unassigned
• Reporter: Thanh Do
• Created: 08/Sep/10 02:01
• Updated: 30/Jul/14 23:50
• Resolved: 30/Jul/14 23:50

Description

We saw a case that NN keeps giving client nodes from the same rack, hence an exception
from client when try to setup the pipeline. Client retries 5 times and fails.

Here is more details. Support we have 2 rack

• Rack 0: from dn1 to dn7
• Rack 1: from dn8 to dn14

Client asks for 3 dns and NN replies with dn1, dn8 and dn9, for example.
Because there is network partition, so client doesn't see any node in Rack 0.
Hence, client add dn1 to excludedNodes list, and ask NN again.
Interestingly, NN picks a different node (from those in excludedNodes) in Rack 0,
and gives back to client, and so on. Client keeps retrying and after 5 times of retrials,
write fails.

This bug was found by our Failure Testing Service framework:
http://www.eecs.berkeley.edu/Pubs/TechRpts/2010/EECS-2010-98.html
For questions, please email us: Thanh Do ([e-mail]) and
Haryadi Gunawi ([e-mail])