Aklakan commented on PR #3184:
URL: https://github.com/apache/jena/pull/3184#issuecomment-3092539788
The original code integrated exec tracking into the
Update-/QueryEngineFactory system. However, this was sub-par because execution
could only be intercepted on the QueryIterator level.
My updated proposal is to introduce a new layer Update-/QueryDispatcher on
top of the Update-/QueryEngineFactory machinery. Now it is possible to
intercept any query / update request to a dataset - even without having to
parse the query.
Old design: QueryExecBuilderDataset -build-> QueryExecDataset -exec->
QueryEngineRegistry
New design: QueryExecBuilderDataset -build-> **QueryDispatcherRegistry**
-customized build-> QueryExec
The returned QueryExec may be of any type, such as a tracking wrapper - it
is no longer necessarily a QueryExecDataset.
Consequences:
* Code that relies on QueryExecBuilderDataset to always return a
QueryExecDataset may break when adding custom interceptors. This should be a
low price to pay because usually one should rely on the QueryExec interface.
* Execution Tracking can be added without any change to the existing code.
## Related Ongoing Work
As a demo for related work based on this infrastructure, we are using it to
integrate third party triple stores - such as Qlever - into Fuseki. This way we
can use one server framework to manage several triple stores.
Technically, we created a DatasetGraph wrapper implementation that is backed
by a factory of HTTP RDFConnection instances (such as to a remote Qlever
database). The query dispatcher just forwards query/update requests to an
RDFConnection obtained from such a DatasetGraph implementation.
Any opinions on this design?
As a final note, we also already created an assembler that starts qlever
from a docker image as part of Fuseki (via the Java TestContainer framework),
so the configuration looks like this:
```turtle
<#baseDS> rdf:type qlever:Dataset ;
qlever:location "/run/databases/qlever/mydb/" ;
qlever:indexName "myindex" ;
qlever:accessToken "abcde" ;
qlever:memoryMaxSize "4G" ;
qlever:defaultQueryTimeout "600s" ;
```
[Example of Qlever in
Fuseki](https://data.aksw.org/#/dataset/text2sparql-2025-dbpedia-qlever/query?query=SELECT%20%28COUNT%28%2A%29%20AS%20%3Fc%29%20%7B%20%3Fs%20%3Fp%20%3Fo%20%7D)
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