As a follow on, I have been looking for a simpler solution.
I have a custom storage to an underlying document store, each document
represents a single subject and contains all triples for that subject.
If I have a query of the form:
select * where { ?subject ns1:predicate2 ns2:subject2 . ?subject ns1:predicate3
ns2:subject3 . ?subject ns1:predicate1 "value1" . }
>From my current understanding and implementation of the custom storage,
>separate calls to find_statements will be made on the storage, with separate
>streams being returned and having to be merged by rasqal/redland.
In the case of my custom storage, it is possible in this case to execute a
single composite query to find subjects that match all three statements.
This would resolve 80-90% of the slow queries we are experiencing and would
cover the initial case where there is a unique match on a string literal, as
the composite query would only return a single subject from the one composite
call.
As far as I can see this composite approach is not currently supported by
storage API.
Extending the storage API would be straight forward, and implementation
optional, but I can not figure out if/how to identify this special case from
the parse tree and pass it through to a storage that supports it.
Any pointers would be appreciated.
Andy
On 12 Feb 2014, at 10:59, Andrew Reslan <[email protected]> wrote:
> Are there any mechanisms in redland/rasqal for reducing query time variance
> depending on statement order in a SPARQL query.
>
> For example a query that contains an exact literal match as the first
> statement, may take a few ms to execute and return a single result.
>
> But if the statement order is changed so that the first statement returns
> 1000's of potential matches then the query time may increases to tens of
> seconds to return the same single result.
>
> I'm trying to find where in the code the execution engine walks the syntax
> tree, and I'm wondering of this could be modified to use a cost based planner
> that could modify the execution order of statements?
>
> Andy
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