[ogsa-wg] OGSA Information Services - Version 3

[guru prasad]

Felix, Donal, Guru,

> Agreed, that paragraph is confusing. (I suspect, but do not know, that
> the information you highlighted was the information produced by the
> "resource-level provider" but that's just my reading...)

Yes, this paragraph is intended to explain the purpose of a resource 
level information provider (for performance reasons it may also have a 
build-in caching). I've changed this part in version 3. Please have a look 
there.

> Comment #2:
> > Does this mean even the resource level information provider is not
> > required??? Or are we saying the service that provides the capability
> > to query is not required????
> > 
> > If the answer to the first question is yes then, I would say it may
> > still be required. Instead of site level information registry getting
> > overloaded with queries about the resources it has, if one has a
> > visibility of a particular resource he could just query that resource.
> 
> I'd say that while the resource-level provider is not a priori required,
> it has to be there conceptually. Sites are free to use other mechanisms
> to actually do the information provision though.
> 
> On the other hand, I really disagree with your second paragraph there.
> One key gain from having a site-level information system is that this is
> a prime location for carrying out queries for resource discovery and
> scheduling. If you require everything to ask the end resources directly,
> then anything that actually needs to look at many resources will end up
> being dog slow because of the amount of network traffic needed to take
> any kind of decision (trust me, I've tried this!) A site-level info
> system is a major optimization, especially if you do not require all
> information within it to be entirely timely.

I figured you'd say this. But somehow I feel that this point should be emphasized in the document. Besides we should also address the case when a new resource is added to a site (where there is already a site level information provider). How will the new resource register or how will the site level information provider discover this new resource. Meaning, is the onus on the resource level provider to advertise or the site level provider to discover. 

Same thing when a resource drops off.

I like the idea of caching. If this is the route we are taking it needs to be put in the document. Then the questions is how frequently the cache is/should be updated? Where will the cache reside? At the host or where the provider is? This needs to go in too.

Finally, how will all this be propagated to Grid level. 


Felix Nikolaus Ehm <felixehm at mail.cern.ch> wrote: 
Hi,

in case you are referring to version 2 of the document:


> Agreed, that paragraph is confusing. (I suspect, but do not know, that
> the information you highlighted was the information produced by the
> "resource-level provider" but that's just my reading...)

Yes, this paragraph is intended to explain the purpose of a resource 
level information provider (for performance reasons it may also have a 
build-in caching). I've changed this part in version 3. Please have a look 
there.



> > Does this mean even the resource level information provider is not
> > required??? Or are we saying the service that provides the capability
> > to query is not required????

The passage wants to express that if a site information system is 
available and provides a common query interface, the resource level 
information components don't necessarily need to implement the same
interface. 
In my opinion their purpose should then be to populate information 
to the site level and not serving external requests.

Concerning the question if the resource level info providers are 
essential INSTEAD of a site-level one I agree with Donal. In the past it 
turned out that caching represents latency, but also protects resources from 
being bombed by requests.  



Felix


On Tue, 7 Aug 2007, Donal K. Fellows wrote:

> guru prasad wrote:
> > I have some corrections and questions. I have highlighted those in the 
> > attached document. Can someone please help me understand.
> 
> Going through your comments (extracted from the document)...
> 
> Comment #1:
> > What information. Information about the resource or the fact that the
> > information provider is on the same host. Too many "This"
> 
> Agreed, that paragraph is confusing. (I suspect, but do not know, that
> the information you highlighted was the information produced by the
> "resource-level provider" but that's just my reading...)
> 
> Comment #2:
> > Does this mean even the resource level information provider is not
> > required??? Or are we saying the service that provides the capability
> > to query is not required????
> > 
> > If the answer to the first question is yes then, I would say it may
> > still be required. Instead of site level information registry getting
> > overloaded with queries about the resources it has, if one has a
> > visibility of a particular resource he could just query that resource.
> 
> I'd say that while the resource-level provider is not a priori required,
> it has to be there conceptually. Sites are free to use other mechanisms
> to actually do the information provision though.
> 
> On the other hand, I really disagree with your second paragraph there.
> One key gain from having a site-level information system is that this is
> a prime location for carrying out queries for resource discovery and
> scheduling. If you require everything to ask the end resources directly,
> then anything that actually needs to look at many resources will end up
> being dog slow because of the amount of network traffic needed to take
> any kind of decision (trust me, I've tried this!) A site-level info
> system is a major optimization, especially if you do not require all
> information within it to be entirely timely.
> 
> Comment #3:
> > Should it say that the developer of the resources could be the
> > information provider ???? This is not clear from the sentence.
> 
> That sentence is wildly unclear, but I suspect it's talking about some
> kind of API for basic info providers to make it easier to write the
> actual information sources. However, I wonder whether this falls more
> within the remit of SAGA - do they do server-side APIs? - since OGSA
> (and related groups) has tended to focus on the wire view of interop.
> 
> Donal.
> --
>   ogsa-wg mailing list
>   ogsa-wg at ogf.org
>   http://www.ogf.org/mailman/listinfo/ogsa-wg
> 


       
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