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https://issues.apache.org/jira/browse/HDFS-7839?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14372146#comment-14372146
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Zhe Zhang commented on HDFS-7839:
---------------------------------
While working on the code I found it hard to store EC policy only on dir level.
NameNode frequently checks this information (e.g. {{getReplication}}) to make
internal decisions. It is too expensive to traverse the namespace for every
such operation (the traversal also requires readLock).
So I guess we need to separately store _desired_ and _actual_ EC policies even
at this stage. Currently the EC policy is binary. My plan is to store desired
policy in dir's XAttr, and get actual policy by checking whether
{{FileWithStripedBlocksFeature}} is set.
As part of HDFS-7337 we'll need to store the EC schema. I guess we can store
the desired schema in dir's XAttr and extend {{FileWithStripedBlocksFeature}}
to store the actual schema.
> Erasure coding: implement facilities in NameNode to create and manage EC zones
> ------------------------------------------------------------------------------
>
> Key: HDFS-7839
> URL: https://issues.apache.org/jira/browse/HDFS-7839
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Zhe Zhang
> Assignee: Zhe Zhang
> Attachments: HDFS-7839-000.patch, HDFS-7839-001.patch
>
>
> As a quick first step to facilitate initial development and testing,
> HDFS-7347 added EC configuration in file header as one storage policy. We
> have discussed and [concluded
> |https://issues.apache.org/jira/browse/HDFS-7285?focusedCommentId=14296210&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14296210]
> that EC configurations should be part of XAttr. This JIRA aims to add the
> basic EC XAttr structure. HDFS-7337 will add configurable and pluggable
> schema info.
> This JIRA will follow the [plan |
> https://issues.apache.org/jira/browse/HDFS-7285?focusedCommentId=14370307&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14370307]
> we made under HDFS-7285.
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