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https://issues.apache.org/jira/browse/HDFS-5434?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Arpit Agarwal updated HDFS-5434:
--------------------------------
Resolution: Fixed
Fix Version/s: 2.4.0
3.0.0
Target Version/s: 2.4.0
Hadoop Flags: Reviewed
Status: Resolved (was: Patch Available)
I committed the latest (5434-branch-2.patch) to trunk and branch-2 for
inclusion in 2.4.
Resolving the Jira as I believe this change allows overriding default placement
for write resiliency.
> Write resiliency for replica count 1
> ------------------------------------
>
> Key: HDFS-5434
> URL: https://issues.apache.org/jira/browse/HDFS-5434
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 2.2.0
> Reporter: Buddy
> Priority: Minor
> Fix For: 3.0.0, 2.4.0
>
> Attachments: BlockPlacementPolicyMinPipelineSize.java,
> BlockPlacementPolicyMinPipelineSizeWithNodeGroup.java,
> HDFS-5434-branch-2.patch, HDFS_5434.patch
>
>
> If a file has a replica count of one, the HDFS client is exposed to write
> failures if the data node fails during a write. With a pipeline of size of
> one, no recovery is possible if the sole data node dies.
> A simple fix is to force a minimum pipeline size of 2, while leaving the
> replication count as 1. The implementation for this is fairly non-invasive.
> Although the replica count is one, the block will be written to two data
> nodes instead of one. If one of the data nodes fails during the write, normal
> pipeline recovery will ensure that the write succeeds to the surviving data
> node.
> The existing code in the name node will prune the extra replica when it
> receives the block received reports for the finalized block from both data
> nodes. This results in the intended replica count of one for the block.
> This behavior should be controlled by a configuration option such as
> {{dfs.namenode.minPipelineSize}}.
> This behavior can be implemented in {{FSNameSystem.getAdditionalBlock()}} by
> ensuring that the pipeline size passed to
> {{BlockPlacementPolicy.chooseTarget()}} in the replication parameter is:
> {code}
> max(replication, ${dfs.namenode.minPipelineSize})
> {code}
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