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https://issues.apache.org/jira/browse/HDFS-12918?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16288485#comment-16288485
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Xiao Chen commented on HDFS-12918:
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Thanks Zach for reporting this and Manoj for investigating.
As Manoj pointed out, I found this too while fixing HDFS-12682. Although it is
a mistake there, it was not changed due to the fear of incompatible behavior,
when discussing whether that should be set to 'DISABLED'.
According to [protobuf
doc|https://developers.google.com/protocol-buffers/docs/proto#optional]: {{If
the default value is not specified for an optional element, a type-specific
default value is used instead...For enums, the default value is the first value
listed in the enum's type definition}}.
I think we check whether a state is set in the protobuf by
{{proto.hasState()}}, so this wrong default shouldn't be visible downstream -
so also echoing Manoj: where is this observed?
> EC Policy defaults incorrectly to enabled in protobufs
> ------------------------------------------------------
>
> 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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