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From Bhavani Ikkurthi ...@tapit.com>
Subject Re: Avro Callback instance and Protocol formats
Date Fri, 24 Feb 2012 17:03:13 GMT
Hi James,

Thanks for the quick response!
I think this is more than enough. Considering your inputs, I will spend
some more time drilling in. I will get back to this email thread with any
more questions that come by my way.


On Fri, Feb 24, 2012 at 11:41 AM, James Baldassari <jbaldassari@gmail.com>wrote:

> Hi Bhavani,
> Regarding the protocol formats, I think you're referring to the difference
> between declaring protocols in JSON and declaring them using the Avro IDL.
> As far as I know there aren't any functional differences between the two
> (i.e. you can do everything in one that you can do in the other), but I
> prefer IDL because I find it to be much more readable.
> When you generate record/protocol code using the Maven, the first step is
> that the Avro Maven plugin is invoked.  If you're interested in seeing this
> code, it's in the avro-maven-plugin module in the Avro source.  The Avro
> Maven plugins parse the protocol and then uses the SpecificCompiler class
> from the avro-compiler project  to generate the interfaces/classes for the
> protocols.  The generated classes will end up in
> target/generated-sources/avro by default.  Keep in mind that if you're
> using an IDE like Eclipse you'll probably have to manually add this
> directory to your project's source path.
> The callback-enabled version of the protocols are generated as
> sub-interfaces of the non-callback protocols.  For example, if you have a
> protocol called Mail, then you'll have a corresponding Java interface
> called Mail, and Mail will have a sub-interface called Mail.Callback.  If
> your generated code has Mail but not Mail.Callback then I think you must be
> using a version of Avro that does not support callbacks.  The callback API
> was introduced in 1.5.2.  Which version are you using?
> I realize that there isn't much documentation about how callbacks work
> other than the JavaDocs.  I'm hoping I'll find the time to write some
> documentation for the Avro website soon.  In the meantime, here are a few
> things to keep in mind:
> - The callback interface only affects the client side of the RPC
> protocol.  The server is always going to implement Mail, but the client has
> the option to use either Mail or Mail.Callback to interact with the server.
> - Only the Netty implementation of the server and transceiver currently
> support asynchronous callbacks.  If you use the callback interface with any
> other transceiver implementation, it will simply behave synchronously.
> - The very first RPC will execute synchronously regardless of whether the
> callback interface is used because the RPC handshake has to be completed,
> but all subsequent RPCs using that Transceiver instance will be
> asynchronous.  See https://issues.apache.org/jira/browse/AVRO-1008 for a
> discussion of this.  (BTW, Doug, I know I owe you a response on this
> ticket.  I'm hoping to get to it soon)
> Let me know if I haven't answered any of your questions.
> -James
> On Fri, Feb 24, 2012 at 11:07 AM, Bhavani Ikkurthi <bi@tapit.com> wrote:
>> Hi,
>> I am pretty much new to using Avro. I started off playing around with
>> James Baldassari's github code: https://github.com/jbaldassari/Avro-RPC
>> I am more interested in Avro's async RPC feature. In that process of
>> creating a Server and Transceiver I encountered few troubles and have the
>> below questions.
>> 1. How does the different Message protocol formats like .avpr/.avdl
>> differ from each other?
>> 2. I am using .avpr file and generating the stubs using "mvn compile"
>> command. Can someone please give me an insight into this compilation
>> process and auto-generation process?
>> 3. Proceeding further, I notice that after generating the code, I cant
>> find a "Callback" interface which I assume is crucial to implementing the
>> async RPC call.
>> I am very new to Avro. So please bear with any techie-term-typos and do
>> take the liberty to correct me. Any help on these questions is much
>> appreciated.
>> --
>> Thanks
>> Bhavani


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