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https://issues.apache.org/jira/browse/HDFS-12918?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Manoj Govindassamy updated HDFS-12918:
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    Summary: NameNode fails to start after upgrade - Missing state in ECPolicy 
Proto   (was: EC Policy defaults incorrectly to enabled in protobufs)

> NameNode fails to start after upgrade - Missing state in ECPolicy Proto 
> ------------------------------------------------------------------------
>
>                 Key: HDFS-12918
>                 URL: https://issues.apache.org/jira/browse/HDFS-12918
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Zach Amsden
>            Assignee: Manoj Govindassamy
>            Priority: Critical
>
> According to documentation and code comments, the default setting for erasure 
> coding policy is disabled:
> /** Policy is disabled. It's policy default state. */
>  DISABLED(1),
> However, HDFS-12258 appears to have incorrectly set the policy state in the 
> protobuf to enabled:
> {code:java}
>  message ErasureCodingPolicyProto {
>     ooptional string name = 1;
>     optional ECSchemaProto schema = 2;
>     optional uint32 cellSize = 3;
>     required uint32 id = 4; // Actually a byte - only 8 bits used
>  + optional ErasureCodingPolicyState state = 5 [default = ENABLED];
>   }
> {code}
> This means the parameter can't actually be optional, it must always be 
> included, and existing serialized data without this optional field will be 
> incorrectly interpreted as having erasure coding enabled.
> This unnecessarily breaks compatibility and will require existing HDFS 
> installations that store metadata in protobufs to require reformatting.
> It looks like a simple mistake that was overlooked in code review.



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