On 26/07/13 09:07, Olivier Rossel wrote:
Usually the author knows the data repartition and can hint the query planer
with some info.
May we such hints could be keywords ahead of the SERVICE keyword.
Example of chaining queries:
SELECT...
WHERE {
SERVICE <foo> {....}
THEN SERVICE <bar> { ... }
}
Example of parallel queries:
SELECT...
WHERE {
SERVICE <foo> {....}
ALSO SERVICE <bar> { ... }
}
... and more.
Sounds silly?
Not silly - with federated query there isn't enough information
available for an optimizer to make sensible choices, and, worse, it's an
area where ordering of operations is much more noticeable (the
operations are inherently more expensive). In practice, I think you
have to give the query writer control.
Andy
