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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8999) Namenode need not wait for {{blockReceived}} for the last block before completing a file.
Date Thu, 21 Jan 2016 13:27:39 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8999?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15110573#comment-15110573
] 

Tsz Wo Nicholas Sze commented on HDFS-8999:
-------------------------------------------

> We now have two places in completeFileInternal to add committed blocks into the pending
queue: one is in commitOrCompleteLastBlock, and the other is addCommittedBlocksToPending.
Do we still need the first one? Looks like we can now remove the changes from HDFS-1172 and
HDFS-9535. 

I think we still need the changes from HDFS-1172 and HDFS-9535 since they add newly COMPLETE
blocks to pending replication.  The current patch adds COMMITTED blocks to pending replication.
 If we remove the changes, the newly COMPLETE blocks won't be added to pending replication.

> 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
>         Attachments: h8999_20151228.patch, h8999_20160106.patch, h8999_20160106b.patch,
h8999_20160106c.patch, h8999_20160111.patch, h8999_20160113.patch, h8999_20160114.patch
>
>
> 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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