perfsonar development work

[Maciej Glowiak <>]

hi Jeff,

Jeff W. Boote wrote:
>  wrote:
> > Author: mac Date: 2006-08-01 10:17:42 -0400 (Tue, 01 Aug 2006) New 
> > Revision:
> > 1504
> >
> > Modified: 
> > trunk/perfsonar/src/org/perfsonar/commons/messages/Request.java Log: 
> > Few changes made.
> >
> > MH doesn't change anything in output requests unless there are multiple
> > responses in one Message. So, if ServiceEngine is run only once for 
> > entire
> > Message (one data trigger), response message is sent without any 
> > changes. If
> > SE was run multiple times, then _0, _1, _2 suffixes will be added to 
> > metadata
> > and data identifiers.
>
> I think this will cause multiple metadata elements that actually refer 
> to the same set of information. Especially given the chaining 
> possibilities.
>
> Think about the RRD MA case where you have a single 'base' metadata 
> indicating the interface information, and then two others chained to it 
> specifying different directions. And two data triggers pointing at 
> these. With this solution, the request for the data for that interface 
> will return a minimum of 4 metadata elements instead of 3. (Could even 
> be more if the service returns all 3 metadata in each service engine 
> response instead of just the two metadata that the data trigger refers 
> to.) The 'base' will not be the same for the two sets of data. I think 
> this could be surprising for clients.
>
> That said, I don't have a better solution unless we constrain services 
> to make metadata id's unique... Then the message handler could just be 
> holding them in a cache and ignore duplicates.
>
> My worry is that a client could easily be counting on determining which 
> data it is looking at by seeing which metadata is referenced. From a 
> client perspective, I would want to be able to see how different pieces 
> of data related to each other in as easy of a way as possible. I think 
> your current solution breaks those relationships.
>
> Can anyone think of another solution? (Is it too burdensome to enforce 
> this uniqueness requirement?) Is any one else worried about the response 
> data no longer having relationship structure maintained?
>
> jeff

Jeff,

The solution with _number has been used for more than 2 months.

1. As you remember, we didn't have generic Message Handler, so everybody 
wrote his own MH. I had to write one for Lookup Service and tried to 
make it quite generic. Then Roman used it for his MAs, but of course 
everybody may use his own MH for his own service.

2. Your case with one common metadata:

   --------------------------------------------------
   <message>

      <metadata id="a"/>
      <metadata id="b" metadataIdRef="a"/>
      <metadata id="c" metadataIdRef="c"/>

      <data metadataIdRef="b"/>
      <data metadataIdRef="c"/>

   </message>
   --------------------------------------------------

   must be split for two sub-requests if we want to run Service Engine
   separate for each data trigger. That's work for both MAs now and for
   LS (except LSRegister which has its own simple Message Handler)

3. Service output is not divided into pieces, so request message from
   pt.2 will cause running Service Engine two times:

   a) request to SE
   --------------------------------------------------
   <message>
      <metadata id="a"/>
      <metadata id="b" metadataIdRef="a"/>
      <data metadataIdRef="b"/>
   </message>
   --------------------------------------------------

   b) request to SE
   --------------------------------------------------
   <message>
      <metadata id="a"/>
      <metadata id="c" metadataIdRef="c"/>
      <data metadataIdRef="c"/>
   </message>
   --------------------------------------------------

   and Service Engine will return similar set of metadatas and datas
   with the same identifiers, for instance:

   a) response from SE
   --------------------------------------------------
   <message>
      <metadata id="X"/>
      <data metadataIdRef="X"/>
   </message>
   --------------------------------------------------

   b) response from SE
   --------------------------------------------------
   <message>
      <metadata id="X"/>
      <data metadataIdRef="X"/>
   </message>
   --------------------------------------------------

   Now, ho do you combine these two into one response message? By
   changing identifiers...

   So the response message will look like:

   --------------------------------------------------
   <message>
      <metadata id="X_1"/>
      <data metadataIdRef="X_1"/>

      <metadata id="X_2"/>
      <data metadataIdRef="X_2"/>
   </message>
   --------------------------------------------------

  And as I said, it works fine. Of course Message handler may be more
  intelligent, but it'd need big effort to implement it, and the final
  effect may also not be satisfied.

  Maciej


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| Maciej Glowiak        Network Research and Development            ||
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     Poznan Supercomputing and Networking Center ||
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