making TAP /async optional.

[Laurent MICHEL]

Hello,

I'd like to come back to Markus's point about the necessity (or not) of 
keeping the /async mode mandatory in TAP.
The /async mode is justified by the necessity of enabling TAP servers to 
process queries consuming a lot of time or resources. The problem is 
that the decision of using one mode or another is taken on the 
client/user side. That supposes the client or the user to have an idea 
about the resources taken by the query or simply to be aware about that 
issue.
Considering that even query engines hardly manage to predict the order 
of magnitude of the query processing duration, I believe that giving the 
choice to users is not really helpful.
Taphandle works around that issue by hiding this choice. It always using 
the /async mode (when it is supported). If the requested data comes 
within 10sec it is displayed as if the query was processed in /sync mode.
In my opinion, the choice of the sync mode should be under the 
responsibility of the server which would just have to notify the client 
that its job has been switched in /async mode (only concerning servers 
implementing such an advanced feature).

A possible evolution of TAP could be to support a third sync mode 
/autosync (no better name comes) which would behave exactly as /sync for 
servers not supporting asynchronous processing or for queries responding 
quickly. Otherwise, when a job is processed in /async mode, the query 
response would be similar to that specified by the actual  /async mode.
The impact for the client would be limited. It would just have to 
distinguish responses containing data from responses containing the 
description of an /async job (to be defined).
Both /sync and /autosync would be mandatory.


Laurent

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