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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1077) namenode RPC protocol method names are overloaded
Date Tue, 06 Apr 2010 00:36:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12853620#action_12853620
] 

Doug Cutting commented on HDFS-1077:
------------------------------------

> However, if a server implements multiple independent RPC protocols, then we cannot require
their method names to not conflict.

Currently Hadoop relies on Java interface semantics: if a service implements two interfaces
with methods of the same signature (unqualified name + param types) then they're collapsed
into a single method in the implementation.  Avro reflect's implementation is similar, except
equality is not on signature but of method name, since Avro supports evolution of message
parameters.

> Aren't the method name prefixed by the protocol name?

In Avro a service could determine which protocol each call belongs to.  But in Hadoop we've
implemented servers that respond to all the methods of numerous protocols, distinguished by
method name and parameter types, not by protocol.  Avro reflect, for compatibility, has followed
this convention.  We could instead, e.g., dispatch each service to a different server-side
object based on the protocol, but that would require much more extensive changes to Hadoop.

> namenode RPC protocol method names are overloaded
> -------------------------------------------------
>
>                 Key: HDFS-1077
>                 URL: https://issues.apache.org/jira/browse/HDFS-1077
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: name-node
>            Reporter: Doug Cutting
>            Assignee: Doug Cutting
>
> Avro RPC does not permit two different messages with the same name.  Several namenode
RPC protocol method names are overloaded.

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