Hi Aaron,
On 28/03/16 17:21, Aaron D. Mihalik wrote:
Two things:
1. Rya will reject a blanket ?s ?p ?o query in order to avoid a full table
scan (even if the G is set).
That's what I thought.
Thanks again.
Brian
2. Here's the code where the specific graph is set [1]. Rya sets the
"ColumnFamily" value on the Accumulo scanner. This filtering/seeking is
all performed on the Accumulo Tablet server.
--Aaron
[1]
https://github.com/apache/incubator-rya/blob/develop/dao/accumulo.rya/src/main/java/mvm/rya/accumulo/query/AccumuloRyaQueryEngine.java#L370
On Sat, Mar 26, 2016 at 8:19 AM Brian McBride <[email protected]> wrote:
Aaron replied:
[[
No... it does not.
We've run into extreme use cases where a graph is created for each
statement (as means of providing properties for a statement). In that
case, Accumulo would not be happy if Rya created a locality group for each
graph.
--Aaron
]]
Again, thanks Aaron. I can see that Accumulo would not be happy in
those circumstances.
I've been trying to understand how Rya handles named graphs. To me it
looks like it treats them as a filter on the results of matching S P O
patterns. Since there is no index that includes the G component of a
quad, and locality groups are not used, I don't see how Rya can limit
its scans to a specific graph. To scan a specific graph, it would have
to scan all the matching triples and filter out the ones from the
specific graph. Is that right? Or is there some Accumulo magic I've
missed.
Queries like
SELECT * { graph <http://example.org/foo> { ?s ?p ?o } }
fail with an exception.
A query like
SELECT DISTINCT ?c { graph <http://example.org/foo> { ?s a ?c } }
will scan all the rdf:type quads in the store, not just those in the
specified graph. (Is that right?)
Is this by design, or does it just reflect the current state of
development?
Brian
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--
Epimorphics Ltd, http://www.epimorphics.com
Registered address: Court Lodge, 105 High Street, Portishead, Bristol BS20 6PT
Epimorphics Ltd. is a limited company registered in England (number 7016688)
