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https://issues.apache.org/jira/browse/HDFS-9579?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15178651#comment-15178651
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Mingliang Liu commented on HDFS-9579:
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Thanks for updating the patch, [~mingma]! I like the idea to make
{{BlockReader}} distance aware and to make {{ReaderStrategy#doRead}} update the
stats in base class.
# Should we remove the stats updating from {{DFSStripedInputStream}} as
{{ReaderStrategy#doRead}} is implicitly called?
{code:title=DFSStripedInputStream.java#readWithStrategy()}
if (dfsClient.stats != null) {
dfsClient.stats.incrementBytesRead(result);
}
{code}
# Nit: After 1 is fixed, perhaps we can make {{DFSClient.stat}} private. I'm
not sure about this but: _a)_ It's {{FileSystem#Statistics}} that is accessed
by up level frameworks _b)_ It's not used elsewhere
# Nit: {{RemoteBlockReader#networkDistance}} and
{{RemoteBlockReader2#networkDistance}} seem {{final}}.
> Provide bytes-read-by-network-distance metrics at FileSystem.Statistics level
> -----------------------------------------------------------------------------
>
> Key: HDFS-9579
> URL: https://issues.apache.org/jira/browse/HDFS-9579
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Ming Ma
> Assignee: Ming Ma
> Attachments: HDFS-9579-2.patch, HDFS-9579-3.patch, HDFS-9579-4.patch,
> HDFS-9579-5.patch, HDFS-9579-6.patch, HDFS-9579-7.patch, HDFS-9579-8.patch,
> HDFS-9579.patch, MR job counters.png
>
>
> For cross DC distcp or other applications, it becomes useful to have insight
> as to the traffic volume for each network distance to distinguish cross-DC
> traffic, local-DC-remote-rack, etc.
> FileSystem's existing {{bytesRead}} metrics tracks all the bytes read. To
> provide additional metrics for each network distance, we can add additional
> metrics to FileSystem level and have {{DFSInputStream}} update the value
> based on the network distance between client and the datanode.
> {{DFSClient}} will resolve client machine's network location as part of its
> initialization. It doesn't need to resolve datanode's network location for
> each read as {{DatanodeInfo}} already has the info.
> There are existing HDFS specific metrics such as {{ReadStatistics}} and
> {{DFSHedgedReadMetrics}}. But these metrics are only accessible via
> {{DFSClient}} or {{DFSInputStream}}. Not something that application framework
> such as MR and Tez can get to. That is the benefit of storing these new
> metrics in FileSystem.Statistics.
> This jira only includes metrics generation by HDFS. The consumption of these
> metrics at MR and Tez will be tracked by separated jiras.
> We can add similar metrics for HDFS write scenario later if it is necessary.
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