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https://issues.apache.org/jira/browse/HDFS-5448?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13812962#comment-13812962
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Eric Sirianni commented on HDFS-5448:
-------------------------------------
Arpit - thanks for the change. The current point of UUID initialization still
leaves a lengthy window during DataNode startup where UUID is null:
{code}
private void connectToNNAndHandshake() throws IOException {
// ...
// FsDatasetInitialization happens as a side effect of this call
bpos.verifyAndSetNamespaceInfo(nsInfo);
// Datanode.checkDatanodeUuid() happens as a side effect of this call
register();
}
{code}
Would it be possible to simply initialize the UUID immediately in the
{{DataStorage}} constructor and then overwrite it from the actual properties
file later via {{setFieldsFromProperties()}} (in the normal case when this is
not the first time the DataNode has started).
(I realize we've moved a bit now from the original JIRA, but it seems
reasonable to take care of this as part of this change)
> Datanode should generate its ID on first registration
> -----------------------------------------------------
>
> Key: HDFS-5448
> URL: https://issues.apache.org/jira/browse/HDFS-5448
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode
> Affects Versions: Heterogeneous Storage (HDFS-2832)
> Reporter: Arpit Agarwal
> Assignee: Arpit Agarwal
> Fix For: Heterogeneous Storage (HDFS-2832)
>
> Attachments: h5448.01.patch, h5448.03.patch, h5448.04.addendum.patch,
> h5448.04.patch
>
>
> Prior to the heterogeneous storage feature, each Datanode had a single
> storage ID which was generated by the Namenode on first registration. The
> storage ID used fixed Datanode identifiers like IP address and port, so that
> in a federated cluster, for example, all NameNodes would generate the same
> storage ID.
> With Heterogeneous storage, we have replaced the storage ID with a
> per-datanode identifier called the Datanode-UUID. The Datanode UUID is also
> assigned by a NameNode on first registration. In a federated cluster with
> multiple namenodes, there are two ways to ensure a unique Datanode UUID
> allocation:
> # Synchronize initial registration requests from the BPServiceActors. If a
> Datanode UUID is already assigned we don't need to synchronize.
> # The datanode assigns itself a UUID on initialization.
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