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https://issues.apache.org/jira/browse/HDFS-14272?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16777406#comment-16777406
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Erik Krogen commented on HDFS-14272:
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[~shv]:
{code}
Since proxies to individual NNs have not been created yet, changeProxy() will
create proxy for the corresponding NN, then call getHAServiceState() and cache
the state. Then it will proceed with the msync() call, which is not needed
because the client already knows the state of that NN.
{code}
Yes, the {{changeProxy()}} within ORPP will call {{getHAServiceState()}}. If an
{{msync()}} was subsequently sent over this proxy, I agree it would be somewhat
redundant. However, {{msync()}} is called on the {{failoverProxy}}, which is a
CFPP. The {{changeProxy()}} method on CFPP will _not_ call
{{getHAServiceState()}}; the {{msync()}} method is the first call that is
performed on the proxy. Thus the number of RPC calls is identical. Whether
those RPCs are calls to {{getHAServiceState()}} or {{msync()}} is not important
for performance, and re-using the {{msync()}} functionality is cleaner IMO.
[~csun]: thanks for the comments, I uploaded v002 addressing them.
> [SBN read] ObserverReadProxyProvider should sync with active txnID on startup
> -----------------------------------------------------------------------------
>
> Key: HDFS-14272
> URL: https://issues.apache.org/jira/browse/HDFS-14272
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: tools
> Environment: CDH6.1 (Hadoop 3.0.x) + Consistency Reads from Standby +
> SSL + Kerberos + RPC encryption
> Reporter: Wei-Chiu Chuang
> Assignee: Erik Krogen
> Priority: Major
> Attachments: HDFS-14272.000.patch, HDFS-14272.001.patch,
> HDFS-14272.002.patch
>
>
> It is typical for integration tests to create some files and then check their
> existence. For example, like the following simple bash script:
> {code:java}
> # hdfs dfs -touchz /tmp/abc
> # hdfs dfs -ls /tmp/abc
> {code}
> The test executes HDFS bash command sequentially, but it may fail with
> Consistent Standby Read because the -ls does not find the file.
> Analysis: the second bash command, while launched sequentially after the
> first one, is not aware of the state id returned from the first bash command.
> So ObserverNode wouldn't wait for the the edits to get propagated, and thus
> fails.
> I've got a cluster where the Observer has tens of seconds of RPC latency, and
> this becomes very annoying. (I am still trying to figure out why this
> Observer has such a long RPC latency. But that's another story.)
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