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https://issues.apache.org/jira/browse/HDFS-8999?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14729407#comment-14729407
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Daryn Sharp commented on HDFS-8999:
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My rhetorical question to provoke thought was misunderstood. I was not
implying we should eliminate IBRs. They do fix data inconsistency and ensure
the NN stays in sync with the DNs state. I would never rely on the client as
an authoritative source of what's on a DN.
bq. So one of the motivations for this simplification is to decrease the total
number of messages sent from DNs to NN. Recently we saw in a real cluster
because a large amount of writing was happening, the IBR from DNs finally
overwhelmed NN and caused congestion of the RPC queue.
Happens all the time. Ironically I've been testing a patch to aggregate IBRs.
No pipeline or DN changes necessary.
> 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
>
> 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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