Re: sparql engine execution hints

I am currently using bigdata and they have exactly this:

http://wiki.bigdata.com/wiki/index.php/QueryHints

fortunately I do not need them very often


I think there are various issues:
a) you write query hints in light of behavior of performance issues with a particular implementation, so hints are generally not very portable
b) it would be good if there was agreement as to the syntax of hints, so that different implementations could at least ignore irrelevant hints
c) in practice, one also rearranges the query to improve performance - and an omniscient optimizer could do that for you … and one implementations optimization is another's slow-down

Jeremy J Carroll
Principal Architect
Syapse, Inc.



On Mar 24, 2014, at 6:45 AM, Jürgen Jakobitsch <j.jakobitsch@semantic-web.at> wrote:

> hi,
> 
> has this already been discussed (is it a good idea?) 
> to include hints for the sparql engine what to execute first?
> 
> i know that every engine has optimizer that do their best, but sometimes
> i just do know better :-)
> 
> in such cases i wouldn't actually want to change my triple store to find 
> the one that executes the query the way i like it.
> 
> one such use case would be from the realm of federated queries where i can 
> move local stuff in the query to the same level of the service keyword by using 
> a subquery (according to spec). but what would be executed first subquery or service?
> 
> any pointer to previous discussions and/or comments highly welcome.
> 
> wkr jürgen
> 
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