Hi Andy,
Thanks for the response. It's tested on Jena 3.10.0 and 3.17.0 on HDD TDB1 -
UNION query counts 63966 results in 1.1s while pipe query finished with timeout
after 2 minutes. Whole dataset has 1322457 triples.
Thanks,
On 2021/02/22 14:01:57, Andy Seaborne <a...@apache.org> wrote:
> Hi Adam,
>
> It would be useful to also know:
>
> which version of Jena this is
> What the storage is - in-memory, or TDB
> TDB1 or TDB2?
> If TDB: What the hardware is disk or SSD?
> What the times actually are and what the count result is?
>
> Count is handled specially in TDB and maybe that interacts with the "|"
> usage.
>
> Andy
>
> On 22/02/2021 13:18, Adam K wrote:
> > Hi all, I executed two simple equivalent queries having a big performance
> > difference on a large dataset:
> >
> >
> > 1. First matching by two alternative predicates using pipe operator
> > * SELECT (count(*) as ?total) WHERE { *
> > * { ?s <http://someURI1 <http://someURI1>> | <http://someURI1
> > <http://someURI1>> ?o .}*
> > * }*
> > this one is very slow and query plan shows the following matching
> > pattern:
> > (path ?subject (alt <http://someURI1> <http://someURI2> ) ?object)))))
> > 2. If I use UNION operator instead of pipe the query becomes fast
> > * SELECT (count(*) as ?total) WHERE {*
> > * { ?s <http://someURI1 <http://someURI1>> ?o . }** UNION** { ?s
> > <http://someURI2 <http://someURI2>> ?o . }*
> > * }*
> > query plan here is different and shows UNION of two BGP matches:
> > (union (bgp (triple ?s <http://someURI1> ?o )) (bgp (triple ?s <
> > http://someURI2> ?o ))))))
> >
> >
> > Documentation here
> > https://jena.apache.org/documentation/query/property_paths.html tells that:
> >
> > 1. "Paths are “simple” if they involve only operators / (sequence), ^
> > (reverse, unary or binary) and the form {n}, for some single integer n."
> > 2. "A path is “complex” if it involves one or more of the operators
> > *,?, + and {}."
> >
> > These statements do do define implications of | - it should act like union,
> > but query plan is different - is it a bug or a feature? Is there general
> > recommendation to use UNION instead of pipe?
> >
> > Thanks for help!
> >
>
