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https://issues.apache.org/jira/browse/HDFS-5167?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13877800#comment-13877800
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Jing Zhao commented on HDFS-5167:
---------------------------------

Thanks for the work [~ozawa]!

bq.  I confirmed that TestLossyRetryInvocationHandler doesn't create 
LossyRetryInvocationHandler by using debugger. Is this assumed code path?
Yes, the test wants to make sure setting lossy retry will not affect the server 
side (i.e., NN). Originally if we set 
DFS_CLIENT_TEST_DROP_NAMENODE_RESPONSE_NUM_KEY to a positive number the NN 
would has some issue (NN will start a DFSClient instance internally for trash 
emptier). We fixed this bug and added this unit test to verify.

bq. 2. I confirmed that we cannot use LossyRetryInvocationHandler just by 
setting
I checked your test code. I think the missing part is that we need to call 
HATestUtil#setFailoverConfigurations to enable HA in the client's 
configuration. Otherwise even if we set the drop response number to 1000, 
NameNodeProxies#createProxyWithLossyRetryHandler will still return null since 
it cannot find a correct FailoverProxyProvider.



> Add metrics about the NameNode retry cache
> ------------------------------------------
>
>                 Key: HDFS-5167
>                 URL: https://issues.apache.org/jira/browse/HDFS-5167
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: ha, namenode
>    Affects Versions: 3.0.0, 2.4.0
>            Reporter: Jing Zhao
>            Assignee: Tsuyoshi OZAWA
>            Priority: Minor
>         Attachments: HDFS-5167.1.patch, HDFS-5167.10.patch, 
> HDFS-5167.2.patch, HDFS-5167.3.patch, HDFS-5167.4.patch, HDFS-5167.5.patch, 
> HDFS-5167.6.patch, HDFS-5167.6.patch, HDFS-5167.7.patch, HDFS-5167.8.patch, 
> HDFS-5167.9-2.patch, HDFS-5167.9.patch
>
>
> It will be helpful to have metrics in NameNode about the retry cache, such as 
> the retry count etc.



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