[occi-wg] confusion about status of link / headers
adrian at jclouds.org
Tue Oct 20 00:19:58 CDT 2009
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 :)
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>
>> 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:
>> 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.
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