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https://issues.apache.org/jira/browse/HADOOP-9421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13690051#comment-13690051
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Luke Lu commented on HADOOP-9421:
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bq. In a world of multiple auths and multiple mechanisms for an auth, requiring 
REINITIATE penalties is too expensive.

If a client can't pick a mechanism, it could skip the initial token and send an 
empty INITIATE, REINITIATE is then not expensive, i.e. exactly equivalent to 
yours.

Hadoop RPC foremost should serve its most common workload: delegation tokens. A 
performance regression for the most common workload in the name of integration 
is not acceptable. The specific optimization for Digest-MD5 (cramming a 
speculative challenge with a negotiate) doesn't work with modern client 
initiated auths like SCRAM. If we have to replace Digest-MD5 for security 
reasons, we'll be SOL. 

bq. Ignoring all the issues I've cited, your optimization doesn't appear to 
have a positive impact on performance.

There is no optimization my patch, which merely leave the door for future 
optimization. In fact, there is performance bug in my impl for Kerberos. It's 
you who added a speculative optimization for Digest-MD5 that doesn't work with 
its future replacement SCRAM.

bq. I feel like we've spent weeks haggling over an ill-suited pre-mature 
optimization that could been spent building upon this implementation.

I merely want to leave the optional client initiate proto *in the protocol* for 
future optimizations. I feel like being forced to implement the optimization to 
show that it's straight forward and incremental.
                
> Convert SASL to use ProtoBuf and add lengths for non-blocking processing
> ------------------------------------------------------------------------
>
>                 Key: HADOOP-9421
>                 URL: https://issues.apache.org/jira/browse/HADOOP-9421
>             Project: Hadoop Common
>          Issue Type: Sub-task
>    Affects Versions: 2.0.3-alpha
>            Reporter: Sanjay Radia
>            Assignee: Daryn Sharp
>            Priority: Blocker
>         Attachments: HADOOP-9421.patch, HADOOP-9421.patch, HADOOP-9421.patch, 
> HADOOP-9421.patch, HADOOP-9421.patch, HADOOP-9421.patch, HADOOP-9421.patch, 
> HADOOP-9421.patch, HADOOP-9421-v2-demo.patch
>
>


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