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From Rob Godfrey <rob.j.godf...@gmail.com>
Subject Re: Question on amqp 1.0 payload Type ??
Date Fri, 02 Aug 2013 12:21:52 GMT
If you are sending a stream of data and you don't know how big it is, then
you cannot use an amqp-value until you have all the data buffered as every
AMQP datatype is encoded either with a fixed size or with the size as a
prefix.  If there is more than 4Gb of data you cannot sent it at all.


As Gordon pointed out, the key difference is in section 3.2:


   -

   The body consists of one of the following three choices: one or
more data<http://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-messaging-v1.0-os.html#type-data>
sections,
   one or more amqp-sequence<http://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-messaging-v1.0-os.html#type-amqp-sequence>
sections,
   or a single amqp-value<http://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-messaging-v1.0-os.html#type-amqp-value>
    section.


You can only have a single amqp-value section, but one or more
amqp-sequence or data

With Data sections you can send multiple sections, with the section
boundaries themselves not having any semantic meaning.  Similarly if you
are sending a sequence of objects, to use a list encoding you need to know
the count and size before sending can commence, with a amqp-sequence you
can send a number of sequence sections as the objects become available.

A different design choice might have been to enable multiple amqp-value
sections, but the implied semantic is different: a series of binary strings
string1, string2, string3 each in separate amp-values would not be the same
as a single binary string string1string2string3.

-- Rob

On 2 August 2013 13:37, Rakesh Kushwaha <kushwaha.r@gmail.com> wrote:

> Hi Rob,
>
> streaming or large message transfer is enabled by just enabling <more=
> true>  in transfer frame .
>
>  for Amqp sequence , amqp specification says* "A sequence section
> contains an arbitrary number of structured data elements". *
>  as parent type of amqp sequence is LIST  which is a compound data type
> will have size encoded for this data type .
> streaming can be implemented  transfer frame 's <more=true> if we can't
> send whole list elements in one go as I understand.
>
> For DATA type also above holds true as per my understanding .
>
> I can't related your answer through amqp specification here ,
>
> Now for amqp value specfication says "An* amqp-value section contains a
> single AMQP value." *
> if size of this amqp value is more than then also streaming may be
> required . what i don't understand is what this "* single AMQP value"
> means. (Number 1 confusion)*
>
> *as amqp value parent type *(any type) ,ideally this can include any
> thing "primitives types , described typed , compound types". if * is
> replaced by list then it can have multiple elements .*
>
> *and if * can replaced by Binary then it can have DATA also.*
> *
> *
>
> *
> *
> <type name="data" class="restricted" source="binary" provides="section">*
> *
> <type name="amqp-sequence" class="restricted" source="list"
> provides="section">
> <type name="amqp-value" class="restricted" source="*" provides="section">
>  // here * can be both list, binary.
>
> ** means any type why we need DATA and SEQUENCE (number 2 confusion).*
> *:)*
> *Regards,*
> *Rakesh*
>
>
>
> *
> *
> *Regards,*
> *Rakesh*
> *
> *
> *
> *
> *
> *
>
>
>
>
>
>
>
>
>
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>
>
> On Fri, Aug 2, 2013 at 1:40 PM, Rob Godfrey <rob.j.godfrey@gmail.com>wrote:
>
>> On 2 August 2013 09:35, Rakesh Kushwaha <kushwaha.r@gmail.com> wrote:
>>
>> > My Question was on format , if for amqp value we have <source=*> that
>> means
>> > it can have both BINARY and LIST kind data type .
>> >
>> > then why we needed DATA and AMQP SEQUENCE .
>> >
>> >
>> As I answered before: data and sequence allow for the case where the size
>> of the data is not known up front by the sending application. AmqpValue
>> requires that you know the size before sending.
>>
>> -- Rob
>>
>>
>> > Regards,
>> > Rakesh
>> >
>> >
>> > On Thu, Aug 1, 2013 at 6:54 PM, Rob Godfrey <rob.j.godfrey@gmail.com>
>> > wrote:
>> >
>> > > Yes indeed Gordon, thank you for clarifying
>> > >
>> > > -- Rob
>> > >
>> > >
>> > > On 1 August 2013 15:01, Gordon Sim <gsim@redhat.com> wrote:
>> > >
>> > > > On 08/01/2013 01:52 PM, Rob Godfrey wrote:
>> > > >
>> > > >> Data and AmqpSequence allow the sender to start sending data
>> without
>> > > >> knowing how many bytes / values the data is going to consist of.
>>  This
>> > > >> allows for streaming scenarios where the size of the data is not
>> known
>> > > up
>> > > >> front.
>> > > >>
>> > > >> Note also that there is no bound to the size of Data or
>> AmqpSequence,
>> > > >> whereas an AmqpValue will always be bounded by the largest AMQP
>> data
>> > > type
>> > > >> -
>> > > >> i.e. 4Gb (not that I would ever recommend sending a single message
>> of
>> > > >> greater than 4Gb).
>> > > >>
>> > > >
>> > > > Just to clarify, each individual section of type Data or
>> AmqpSequence
>> > is
>> > > > bounded and has its size encoded upfront. The ability to stream
>> and/or
>> > > send
>> > > > unbounded amounts of data comes through sending multiple such
>> sections
>> > in
>> > > > the same message. Right? (Whereas only a single AmqpValue section
is
>> > > > allowed per message).
>> > > >
>> > > >
>> > > >
>> >
>> ------------------------------**------------------------------**---------
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>> > > >
>> > > >
>> > >
>> >
>>
>
>

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