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https://issues.apache.org/jira/browse/HDFS-5051?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13739707#comment-13739707
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Suresh Srinivas commented on HDFS-5051:
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bq. The random jitter code was taken from the block report code. The goal is
the same-- to avoid overloading the NameNode with too many reports at the same
time. I don't see any reason to take out the jitter code here, although it will
not be as important as it was in the block report case.
Quoting my own question:
bq. When a datanode starts, do we expect any thing to be in the cache at all?
Hence the question why is jitter code is important?
bq. They aren't included in the regular block report in StorageBlockReportProto.
That is not correct. Please see the code in BlockListAsLongs.
We need to decide the following (and I do not think with the current summary in
HDFS-5053, that is the right place):
# Do we need to include generation stamp and length? My early thought is, it
may not be necessary. Current code includes both generation stamp and length.
# When there are no cache entries in the datanode, my preference is not to send
a cache report at all, including the first time datanode starts up. I agree
that we could have incremental cache report.
> Propagate cache status information from the DataNode to the NameNode
> --------------------------------------------------------------------
>
> Key: HDFS-5051
> URL: https://issues.apache.org/jira/browse/HDFS-5051
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode, namenode
> Reporter: Colin Patrick McCabe
> Assignee: Andrew Wang
> Attachments: hdfs-5051-1.patch, hdfs-5051-2.patch
>
>
> The DataNode needs to inform the NameNode of its current cache state. Let's
> wire up the RPCs and stub out the relevant methods on the DN and NN side.
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