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https://issues.apache.org/jira/browse/HDFS-4212?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13565884#comment-13565884
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Suresh Srinivas commented on HDFS-4212:
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bq. Brandon. The problem mentioned in your original description seems not to be
a problem at all. Because client never knows whether block was created or not
until it gets a reply from NN. If NN crashes before replying the block will be
correctly reported as missing on restart if it was created. This is the nature
of distributed computing.
Actually it is a problem related to HDFS-4452. When client does not block was
create or not, it retries. As getAdditionalBlock() stands currently, it is
really not idempotent. I think adding getAdditionalBlock at an offset as
suggested by Brandon will make it idempotent. Hence on retry, for the same
offset, from the same client, namenode can return the block that has been
allocated, instead of creating new ones.
> NameNode can't differentiate between a never-created block and a block which
> is really missing
> ----------------------------------------------------------------------------------------------
>
> Key: HDFS-4212
> URL: https://issues.apache.org/jira/browse/HDFS-4212
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 1.2.0, 3.0.0
> Reporter: Brandon Li
> Assignee: Brandon Li
> Attachments: hdfs-4212-junit-test.patch
>
>
> In one test case, NameNode allocated a block and then was killed before the
> client got the addBlock response.
> After NameNode restarted, the block which was never created was considered as
> a missing block and FSCK would report the file is corrupted.
> The problem seems to be that, NameNode can't differentiate between a
> never-created block and a block which is really missing.
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