[HDFS-9837] BlockManager#countNodes should be able to detect duplicated internal blocks

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.0.0-alpha1
• Fix Version/s: 3.0.0-alpha1
• Hadoop Flags: Reviewed
• Assignee: Jing Zhao
• Reporter: Jing Zhao
• Created: 19/Feb/16 22:44
• Updated: 12/May/16 18:16
• Resolved: 24/Feb/16 23:15

Description

Currently BlockManager#countNodes only counts the number of replicas/internal blocks thus it cannot detect the under-replicated scenario where a striped EC block has 9 internal blocks but contains duplicated data/parity blocks. E.g., b8 is missing while 2 b0 exist:
b0, b1, b2, b3, b4, b5, b6, b7, b0

If the NameNode keeps running, NN is able to detect the duplication of b0 and will put the block into the excess map. countNodes excludes internal blocks captured in the excess map thus can return the correct number of live replicas. However, if NN restarts before sending out the reconstruction command, the missing internal block cannot be detected anymore. The following steps can reproduce the issue:

1. create an EC file
2. kill DN1 and wait for the reconstruction to happen
3. start DN1 again
4. kill DN2 and restart NN immediately