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From "Alejandro Fernandez" <afernan...@hortonworks.com>
Subject Re: Review Request 36231: Revert, The Default hdfs-site.xml Should Have Client Retry Logic Enabled For Rolling Upgrade
Date Tue, 07 Jul 2015 02:30:24 GMT


> On July 7, 2015, 12:22 a.m., Jonathan Hurley wrote:
> > Won't reverting this patch cause problems with the long running tests?

Basically, HDFS has two layers of retries, and only of them should really be used during HA.
When one NameNode is up, setting dfs.client.retry.policy.enabled to false allows it to quickly
find the active (in the case of HA and when a client tried to connect to the dead NameNode),
or retry for up to 3 mins in non-HA.

Comment from Jing,
"dfs.client.retry.policy.enabled" is only used for client connecting to NameNode so the change
will not affect other components. In the meanwhile, after setting the conf property back to
false, the retry is controlled only by FailoverOnNetworkExceptionRetry, which can retry up
to 10 times and failover 15 times by default. In case that both NameNodes are down because
only one retry policy takes effect the total retry time will be much less compared with the
case we set "dfs.client.retry.policy.enabled" to true. If both NameNodes are in the standby
state the total retry time will not be affected.


- Alejandro


-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/36231/#review90613
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On July 6, 2015, 11:58 p.m., Alejandro Fernandez wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/36231/
> -----------------------------------------------------------
> 
> (Updated July 6, 2015, 11:58 p.m.)
> 
> 
> Review request for Ambari, Jonathan Hurley and Nate Cole.
> 
> 
> Repository: ambari
> 
> 
> Description
> -------
> 
> In the case of an HA cluster where the former primary NN was killed "dirty", by catastrophic
power-down or equivalent, and the cluster has successfully failed over to the other NN, a
client that first attempts to contact the dead NN takes 10 minutes to switch to the other
NN.
> 
> In Ambari 2.0 and HDP 2.2, dfs.client.retry.policy.enabled was not set at all.
> Recently, in Ambari 2.1 for HDP 2.3, it was defaulted to true as part of AMBARI-11192.
> However, this causes problems during RU
> 
> In an HA setup, our retry actually should be handled by RetryInvocationHandler using
retry policy FailoverOnNetworkExceptionRetry. The client first translates the nameservice
ID into two host names, and creates an individual RPC proxy for each NameNode accordingly.
Each individual NameNode proxy still uses MultipleLinearRandomRetry as its local retry policy,
but because we usually set dfs.client.retry.policy.enabled to false, thus this internal retry
is actually disabled. Then in case we hit any connection issue or remote exception (including
StandbyException), the exception is caught by RetryInvocationHandler and handled according
to FailoverOnNetworkExceptionRetry. In this way the client can failover to the other namenode
immediately instead of keeping retrying the same NameNode.
> However, here because we set dfs.client.retry.policy.enabled to true, the MultipleLinearRandomRetry
is triggered inside of the internal NameNode proxy thus we have to wait 10+ min. The exception
is finally thrown to RetryInvocationHandler until all the retries of MultipleLinearRandomRetry
fail.
> 
> 
> Diffs
> -----
> 
>   ambari-server/src/main/java/org/apache/ambari/server/checks/CheckDescription.java 5e029f4

>   ambari-server/src/main/java/org/apache/ambari/server/checks/ClientRetryPropertyCheck.java
4beba33 
>   ambari-server/src/main/resources/stacks/HDP/2.2/services/HDFS/configuration/hdfs-site.xml
e42b3f8 
>   ambari-server/src/test/java/org/apache/ambari/server/checks/ClientRetryPropertyCheckTest.java
d3fd187 
> 
> Diff: https://reviews.apache.org/r/36231/diff/
> 
> 
> Testing
> -------
> 
> Unit tests passed,
> 
> ----------------------------------------------------------------------
> Total run:761
> Total errors:0
> Total failures:0
> OK
> 
> I deployed my changes to a brand new cluster and it correctly set the hdfs-site property
dfs.client.retry.policy.enabled to false.
> 
> 
> Thanks,
> 
> Alejandro Fernandez
> 
>


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