[occi-wg] confusion about status of link / headers

Alexis Richardson alexis.richardson at gmail.com
Tue Oct 20 02:55:16 CDT 2009

What about compute clouds?

On Tue, Oct 20, 2009 at 6:19 AM, Adrian Cole <adrian at jclouds.org> wrote:
> Here are options for metadata used in some of the major storage clouds FWIW:
> S3, Rackspace, EMC Atmos, Azure - Headers
> Nirvanix - query params in, xml entity out
> Mezeo - entity
> Of the ones using headers, S3, Rackspace and Azure use prefix with
> values stored as-us.  Atmos joins all metadata together into one
> header, making parsing trivial (split /,/), but necessary.
> The most expensive option of the above is entity, where each metadata
> value is a separate GET.  However, entities allow binary metadata and
> zero restrictions on it, which may be useful.
> In jclouds, we time parsing of response values.  A simple XML doc with
> only several elements written in SAX takes a few ms to parse.  My log
> files are not precise enough to find the overhead in parsing headers:
> they always start and finish within the same millisecond.
> I hope this background helps, and also helps explain why I'm vocal on
> such topics such as headers vs entities :)
> Cheers,
> -Adrian
> On Mon, Oct 19, 2009 at 4:21 PM, Sam Johnston <samj at samj.net> wrote:
>> On Tue, Oct 20, 2009 at 12:57 AM, gary mazzaferro <garymazzaferro at gmail.com>
>> wrote:
>>> The http header and key/value pairs need to parsed also, there is no free
>>> ride here.
>> Every HTTP library I have ever used parses HTTP headers and puts them in a
>> nice hash for you ready to consume. If we go for "Name: Value" then that's
>> all there is to it. If we go for "Attribute: name=value" as is currently
>> proposed (which is arguably cleaner, follows cookies' "prior art" and avoids
>> Amazon's prefix hack) then you just have to split on '='.
>> To illustrate how clean this is by example:
>>> #!/usr/bin/python
>>> import urllib2
>>> response = urllib2.urlopen('http://cloud.example.com/myvm')
>>> representation = response.read()
>>> metadata = response.info()
>>> print metadata['occi-compute-cores']
>> As soon as you start talking about payloads you have to fire up a parser
>> (JSON/XML/Atom/etc.) or write your own (previous text rendering) which is
>> significantly more work to do at both design and run times. Not to mention
>> more work for us to do now and more scope for interoperability problems.
>> Sam
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