On 24/12/17 14:11, Andrew U. Frank wrote:
thank you for the information; i take that using teh indexes a
one-variable query would be (close to) linear in the amount of triples
found. i saw that TBD does build indexes and assumed they use hashes.
i have still the following questions:
1. is performance different for a named or the default graph?
Query performance is approximately the same for GRAPH.
Update is slower.
2. can i simplify measurements with putting pieces of the dataset in
different graphs and then add more or less of these graphs to take a
measure? say i have 5 named graphs, each with 10 million triples, do
queries over 2, 3, 4 and 5 graphs give the same (or very similar)
results than when i would load 20, 30, 40 and 50 million triples in a
single named graph?
Any measurements would be unreliable at best and probably worthless.
1/ Different data gives different answers to queries.
2/ Caching matters a lot for databases and a different setup will cache
differently.
Andy
thank you for help!
andrew
On 12/23/2017 06:20 AM, ajs6f wrote:
For example, the TIM in-memory dataset impl uses 3 indexes on triples
and 6 on quads to ensure that all one-variable queries (i.e. for
triples ?s <p> <o>, <s> ?p <o>, <s> <p> ?o) will be as direct as
possible. The indexes are hashmaps (e.g. Map<Node, Map<Node,
Set<Node>>>) and don't use the kind of node directory that TDB does.
There are lots of other ways to play that out, according to the
balance of times costs and storage costs desired and the expected
types of queries.
Adam
On Dec 23, 2017, at 2:56 AM, Lorenz Buehmann
<[email protected]> wrote:
On 23.12.2017 00:47, Andrew U. Frank wrote:
are there some rules which queries are linear in the amount of data in
the graph? is it correct to assume that searching for a triples based
on a single condition (?p a X) is logarithmic in the size of the data
collection?
Why should it be logarithmic? The complexity of matching a single BGP
depends on the implementation. I could search for matches by doing a
scan on the whole dataset - that would for sure be not logarithmic but
linear. Usually, if exists, a triple store would use the POS index in
order to find bindings for variable ?p.
Cheers,
Lorenz
