Eric Sirianni created HDFS-5454:
-----------------------------------
Summary: DataNode UUID should be assigned prior to FsDataset
initialization
Key: HDFS-5454
URL: https://issues.apache.org/jira/browse/HDFS-5454
Project: Hadoop HDFS
Issue Type: Bug
Components: datanode
Affects Versions: 2.2.0
Reporter: Eric Sirianni
Assignee: Arpit Agarwal
Priority: Minor
The DataNode's UUID ({{DataStorage.getDatanodeUuid()}} field) is NULL at the
point where the {{FsDataset}} object is created ({{DataNode.initStorage()}}.
As the {{DataStorage}} object is an input to the {{FsDataset}} factory method,
it is desirable for it to be fully populated with a UUID at this point. In
particular, our {{FsDatasetSpi}} implementation relies upon the DataNode UUID
as a key to access our underlying block storage device.
This also appears to be a regression compared to Hadoop 1.x - our 1.x
{{FSDatasetInterface}} plugin has a non-NULL UUID on startup. I haven't fully
traced through the code, but I suspect this came from the
{{BPOfferService}}/{{BPServiceActor}} refactoring to support federated
namenodes.
With HDFS-5448, the DataNode is now responsible for generating its own UUID.
This greatly simplifies the fix. Move the UUID check/generation in from
{{DataNode.createBPRegistration()}} to {{DataNode.initStorage()}}. This more
naturally co-locates UUID generation immediately subsequent to the read of the
UUID from the {{DataStorage}} properties file.
{code}
private void initStorage(final NamespaceInfo nsInfo) throws IOException {
// ...
final String bpid = nsInfo.getBlockPoolID();
//read storage info, lock data dirs and transition fs state if necessary
storage.recoverTransitionRead(this, bpid, nsInfo, dataDirs, startOpt);
// SUGGESTED NEW PLACE TO CHECK DATANODE UUID
checkDatanodeUuid();
// ...
}
{code}
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