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https://issues.apache.org/jira/browse/HDFS-10252?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15222889#comment-15222889
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Vinayakumar B commented on HDFS-10252:
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bq. I spent hours of debugging but I could not find it. Is it somewhere there,
or only the NameNode knows the name of that file?
The answer is NO.
Datanode doesnot know anything about the file name, whose data its going to
store. All it knows is the BlockId.
file->blockId mapping will be present in the NameNode. Datanode just stores the
block with the BlockId, issued by the NameNode to client. And Client writes the
data with the same blockId to datanode.
[~sarigian], If you have any further queries about hdfs internals, instead of
raising Jira. Please subscribe and send a mail to either
[email protected]. I am sure, someone will reply. Jira is to track
issues. If you find any issues during your learning process, please file a jira
ticket.
Subscribing details are at http://hadoop.apache.org/mailing_lists.html.
I am going to close this ticket.
Thanks.
> Is DataNode aware of the name of the file that it is going to store?
> --------------------------------------------------------------------
>
> Key: HDFS-10252
> URL: https://issues.apache.org/jira/browse/HDFS-10252
> Project: Hadoop HDFS
> Issue Type: Test
> Components: datanode, namenode
> Reporter: Dimitrios Sarigiannis
> Priority: Minor
>
> I am going through the HDFS Namenode and Datanode code and I am trying to see
> if the DataNode is aware of the names of the files that are stored in it (and
> other metadata as well).
> Assuming that we have the most simple case:
> 1 NameNode
> 1 DataNode
> 1 single machine running HDFS with replication factor 1.
> and considering the way HDFS works a use case could be:
> A client requests to write a file from local to HDFS (for example: "hdfs dfs
> -put file /file")
> He first communicates with NameNode and gets where this file should be stored.
> Then, after receiving an answer, he requests to the DataNode to store that
> file.
> (At that point I am going to be a little more specific about the code)
> The DataNode has a DataXceiverServer class which runs and waits for requests.
> When a request comes, it starts a DataXceiver thread and try to serve that
> request. What I would like to know is, if at that specific point the DataNode
> knows the name of the file that it is going to store. I spent hours of
> debugging but I could not find it. Is it somewhere there, or only the
> NameNode knows the name of that file?
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