bbeaudreault opened a new pull request #3594:
URL: https://github.com/apache/hadoop/pull/3594


   ### Description of PR
   See https://issues.apache.org/jira/browse/HDFS-16261 for more details.
   
   The most straightforward way to introduce a grace period for replaced blocks 
is in the InvalidateBlocks datastructure. Work is periodically pulled from this 
class to be divvied up to DataNodes. This class is also reported on with JMX 
metrics, so one can easily see how many blocks are currently pending deletion.
   
   I achieved the grace period by adding a new `pollNWithFilter` method to 
`LightWeightHashSet`. InvalidateBlocks are added to the LightWeightHashSet with 
a calculated `readyForDeleteAt` time. When `getBlocksToInvalidateByLimit` is 
called, a filter is passed which only includes those blocks whose 
`readyForDeleteAt` is expired.
   
   The default grace period for blocks added to InvalidateBlocks is 0, which 
effectively makes all blocks immediately ready for deletion per existing 
behavior. When a grace period is configured, it applies only to blocks deleted 
through the `delHintNode` passed in RECEIVED_BLOCK messages. This minimizes the 
impact of this feature on blocks deleted for other reasons (i.e. if a file is 
deleted or through other ongoing namenode auditing).
   
   ### How was this patch tested?
   
   I've added tests for the relevant pieces, and have also been running this on 
2 clusters internally.
   
   ### For code changes:
   
   - [x] Does the title or this PR starts with the corresponding JIRA issue id 
(e.g. 'HADOOP-17799. Your PR title ...')?
   - [ ] Object storage: have the integration tests been executed and the 
endpoint declared according to the connector-specific documentation?
   - [ ] If adding new dependencies to the code, are these dependencies 
licensed in a way that is compatible for inclusion under [ASF 
2.0](http://www.apache.org/legal/resolved.html#category-a)?
   - [ ] If applicable, have you updated the `LICENSE`, `LICENSE-binary`, 
`NOTICE-binary` files?
   
   


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