making TAP /async optional.

[Dave Morris]

Hiya,

On 2014-05-20 00:00, Petr Skoda wrote:
> 
> I think the user should be warned first that the sync queries will
> time out soon after xx seconds - should be in description of TAP
> service clearly stated.
> 
> And that async will run for a longer time - but still limited by server
> The UWS of the TAP service should say directly what is the timeout to
> abort the job.
> 

Something to bear in mind - the time out for a /sync request is not 
necessarily decided by the client or server.

If you are on the same local area network as the web server, then you 
have a good chance of keeping
a HTTP connection open for > 5min waiting for a response.

If you are connecting through multiple hops via one or more content 
filters or HTTP proxies,
then any one of them may get bored and decide to timeout an inactive 
connection.

This can have a big impact on service reliability. Something that 
appears to work fine on the local
LAN may randomly timeout and fail when run via a conference wifi.

TL;DR;
/sync timeout depends on the network
/async is more robust

Markus's summary is about right.

* Use sync if you want immediate results
   (but you may get an error if your request times out)

* Use async if you want reliable delivery
   (but you will have to wait a bit longer)


Hope this helps,
Dave

--------
Dave Morris
Software Developer
Wide Field Astronomy Unit
Institute for Astronomy
University of Edinburgh
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