afs commented on issue #1557:
URL: https://github.com/apache/jena/issues/1557#issuecomment-1262101774
The question was why is the wrong query being asked in the first place. You
say you have no control over the query. Where is it coming from?
The implication I take from all this is that the motivation is "to be like
Virtuoso". That implies all Virtuoso features are replicated. Not
point-by-point. It'll end up going round in a loop next PR.
Virtuoso is RDF 1.0. It has SQL expression evaluation semantics.
> possible to rewrite ANY query UNLESS it makes use of FROM (NAMED)
There is not exception. The operation handlers in the server for all and any
functionality can be replaced. They are not special; they are the default
registrations. Nothing in Fuseki is hardwired except for the dispatch process.
Any query can be transformed in Fuseki. Add a custom operation
implementation and handle the incoming request.
`SPARQLQueryProcessor` provides most of the work if you want to use that;
it is not mandated you do use it. It has several extension points.
`SPARQL_QueryDataset` is very short - the only thing it does is
`decideDataset` - so alternative choices can be implemented and still reuse the
bulk of the query execution machinery (and note `getDataset` - the dataset
found during routing is available).
Specifically to dynamic datasets: it records the original dataset
description so all query information is available.
We still don't know where costs are coming from - only "our datasets" and
"FROM" which is way to far away to point to the code in question. The fact you
are counting (counting is optimized for TDB) matters.
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