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https://issues.apache.org/jira/browse/HADOOP-5724?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12708513#action_12708513
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Suresh Srinivas commented on HADOOP-5724:
-----------------------------------------
bq. I don't think so... the blocks are removed from the datanode list only
after the blockreport. from what I can see, could be mistaken.
Block is indeed deleted from the blocksMap when the file is deleted. The reason
why it works in this case is - if the next block report from the datanode
includes the deleted block, since the corresponding file is not found, the
block is not added to the blocksMap.
To summarize the difference:
When a file is deleted, blocks can be deleted from blocksMap. Non existence
file serves as a reminder that the block is no longer valid. However when a
block gets deleted from a datanode (and the file still exists), there is
nothing on the namenode that indicates that the block has been deleted from the
datanode.
> Datanode should report deletion of blocks to Namenode explicitly
> ----------------------------------------------------------------
>
> Key: HADOOP-5724
> URL: https://issues.apache.org/jira/browse/HADOOP-5724
> Project: Hadoop Core
> Issue Type: Bug
> Reporter: Suresh Srinivas
> Assignee: Suresh Srinivas
> Fix For: 0.21.0
>
> Attachments: blockdel.patch, blockdel.patch
>
>
> Currently datanode notifies namenode newly added blocks and the blocks that
> are corrupt. There is no explicit message from the datanode to the namenode
> to indicate the deletion of blocks. Block reports from the datanode is the
> only way for the namenode to learn about the deletion of blocks at a
> datanode. With the addition of explicit request to indicate to block
> deletion, block report interval (which is currently 1 hour) can be increased
> to a longer duration. This reduces load on both namenode and datanodes.
>
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