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https://issues.apache.org/jira/browse/HADOOP-7557?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13126209#comment-13126209
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Doug Cutting commented on HADOOP-7557:
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> The extra field (protocolKind) I added was to distinguish between the
> multiple PRC Engines and catch bugs when there is a mismatch - this should
> have been done when we added the multiple RPC engines.
I disagree. We need to have two engines: present and future. A developer
should be able to configure things to use future, but only present should ever
be used in production. Our wire format should not be engineered around
supporting multiple wire formats in production. Rather a given release should
support a single wire format. We'll someday switch to future, which supports
inter-version and inter-language compatibility, security, has good performance,
etc. At that point we discard present.
> Essentially you are arguing that IpcHeader does not need to be extensible and
> that essentially we should merge the "hrpc" header and the ipcHeader.
No, the wire format of headers is a property of the protocol engine, not a
universal thing. The existing AvroRpcEngine is a work in progress. It
piggybacks on WritableRpc for its wire protocol as its initial goal was just to
debug just message serialization, then subsequently change the full protocol
wire format, including headers, security, etc. Work on AvroRpcEngine stopped
when e14 vetoed this proposed present/future incremental approach. If that
work were to continue, I might next try to switch AvroRpcEngine to a different
underlying network protocol (e.g., HTTP, Avro's SASL profile, or something new)
that's language independent, has other implementations, etc. Or work could be
done on switching from Avro reflect to specific. But we shouldn't extend the
legacy RPC format to also handle the future format, otherwise we're stuck with
the legacy forever.
> Make IPC header be extensible
> -------------------------------
>
> Key: HADOOP-7557
> URL: https://issues.apache.org/jira/browse/HADOOP-7557
> Project: Hadoop Common
> Issue Type: Improvement
> Reporter: Sanjay Radia
> Assignee: Sanjay Radia
> Attachments: HADOOP-7557.patch, IpcHeader.proto, ipcHeader1.patch,
> ipcHeader2.patch
>
>
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