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From "Jitendra Nath Pandey (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8999) Namenode need not wait for {{blockReceived}} for the last block before completing a file.
Date Fri, 18 Dec 2015 23:40:47 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8999?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15064975#comment-15064975
] 

Jitendra Nath Pandey commented on HDFS-8999:
--------------------------------------------

[~shv], the goal of this jira is to allow closing the files without waiting for IBRs from
DN. This will also reduce the pressure on DNs to quickly send {{blockReceived}} messages,
and allow sending IBRs at longer intervals to reduce the number of RPCs to NN. As mentioned
by [~jingzhao] in an earlier comment, it has been observed in real clusters where IBRs overwhelmed
the NN and clients failed to close the files.

> Namenode need not wait for {{blockReceived}} for the last block before completing a file.
> -----------------------------------------------------------------------------------------
>
>                 Key: HDFS-8999
>                 URL: https://issues.apache.org/jira/browse/HDFS-8999
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>            Reporter: Jitendra Nath Pandey
>            Assignee: Tsz Wo Nicholas Sze
>
> This comes out of a discussion in HDFS-8763. Pasting [~jingzhao]'s comment from the jira:
> {quote}
> ...whether we need to let NameNode wait for all the block_received msgs to announce the
replica is safe. Looking into the code, now we have
>    # NameNode knows the DataNodes involved when initially setting up the writing pipeline
>    # If any DataNode fails during the writing, client bumps the GS and finally reports
all the DataNodes included in the new pipeline to NameNode through the updatePipeline RPC.
>    # When the client received the ack for the last packet of the block (and before the
client tries to close the file on NameNode), the replica has been finalized in all the DataNodes.
> Then in this case, when NameNode receives the close request from the client, the NameNode
already knows the latest replicas for the block. Currently the checkReplication call only
counts in all the replicas that NN has already received the block_received msg, but based
on the above #2 and #3, it may be safe to also count in all the replicas in the BlockUnderConstructionFeature#replicas?
> {quote}



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