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https://issues.apache.org/jira/browse/HDFS-1332?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13033346#comment-13033346
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Todd Lipcon commented on HDFS-1332:
-----------------------------------
Hey Nicholas. How do you feel about the following compromise:
- For the simple case that there are no datanodes in the cluster, we include
some additional detail in the exception message indicating as much. This will
help the common case of a new user whose datanodes failed to start and is
confused why he can't write blocks. This should be in the IOException itself so
that it propagates to the client.
- if debug is enabled, we construct the HashMap as above, and log the "failure
to allocate block" type messages at WARN level
- if debug is not enabled, then we log a message that says something like
"failure to allocate block ... For more information, please enable DEBUG level
logging on the o.a.h.BlockPlacementPolicyDefault logger."
This should avoid any performance impact, but also point users down the right
path to solving the issues.
> When unable to place replicas, BlockPlacementPolicy should log reasons nodes
> were excluded
> ------------------------------------------------------------------------------------------
>
> Key: HDFS-1332
> URL: https://issues.apache.org/jira/browse/HDFS-1332
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: name-node
> Reporter: Todd Lipcon
> Assignee: Ted Yu
> Priority: Minor
> Labels: newbie
> Fix For: 0.23.0
>
> Attachments: HDFS-1332.patch
>
>
> Whenever the block placement policy determines that a node is not a "good
> target" it could add the reason for exclusion to a list, and then when we log
> "Not able to place enough replicas" we could say why each node was refused.
> This would help new users who are having issues on pseudo-distributed (eg
> because their data dir is on /tmp and /tmp is full). Right now it's very
> difficult to figure out the issue.
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