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https://issues.apache.org/jira/browse/HDFS-12943?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16723272#comment-16723272
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Chen Liang commented on HDFS-12943:
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Hi [~brahmareddy],
Thanks for testing! The timeout issue seems interesting. To start with, it is
expected to see some performance degradation *from CLI*, because CLI initiates
a DFSClient every time for each command, a fresh DFSClient has to get status of
name nodes every time. But if it is the same DFSClient being reused, this would
not be an issue. I have never seen the second-call issue. Here is an output
from our cluster (log outpu part omitted), and I think you are right about
lowering dfs.ha.tail-edits.period, we had similar numbers here:
{code:java}
$time hdfs --loglevel debug dfs
-Ddfs.client.failover.proxy.provider.ltx1-unonn01=org.apache.hadoop.hdfs.server.namenode.ha.ObserverReadProxyProvider
-mkdir /TestsORF1
real 0m2.254s
user 0m3.608s
sys 0m0.331s
$time hdfs --loglevel debug dfs
-Ddfs.client.failover.proxy.provider.ltx1-unonn01=org.apache.hadoop.hdfs.server.namenode.ha.ObserverReadProxyProvider
-mkdir /TestsORF2
real 0m2.159s
user 0m3.855s
sys 0m0.330s{code}
** Curious, how many NN you had in the testing? and was there any error from
NN logs?
> Consistent Reads from Standby Node
> ----------------------------------
>
> Key: HDFS-12943
> URL: https://issues.apache.org/jira/browse/HDFS-12943
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: hdfs
> Reporter: Konstantin Shvachko
> Priority: Major
> Attachments: ConsistentReadsFromStandbyNode.pdf,
> ConsistentReadsFromStandbyNode.pdf, HDFS-12943-001.patch,
> HDFS-12943-002.patch, TestPlan-ConsistentReadsFromStandbyNode.pdf
>
>
> StandbyNode in HDFS is a replica of the active NameNode. The states of the
> NameNodes are coordinated via the journal. It is natural to consider
> StandbyNode as a read-only replica. As with any replicated distributed system
> the problem of stale reads should be resolved. Our main goal is to provide
> reads from standby in a consistent way in order to enable a wide range of
> existing applications running on top of HDFS.
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