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From Andy Seaborne <>
Subject Re: Clustering
Date Tue, 23 Jul 2013 14:14:39 GMT
On 22/07/13 09:23, Minto van der Sluis wrote:
> Hi Andy,
> See below
> Regards,
> Minto
> Op 21-7-2013 19:06, Andy Seaborne schreef:
>> Minto,
>> Do you want a shared database across the cluster (3 tier architecture
>> style)?  That's what SDB woulD give you.
> Yes, using a separate DB layer which most probably should be clustered
> itself. Preferred database is postgres. As far as I understand this
> would not be a problem for SDB. But somehow I fear a preformance drop
> when switching to SDB. Is this justified?


Laying over SQL/JDBC and preserving SPARQL (specifically XSD value) 
semantics means a lot of trips to the database for a single query unless 
it is a single graph pattern or graph pattern and OPTIONAL (no FILTERS).

The only SQL-level engines left at scale these days put SPARQL inside 
the SQL engine, not layered on top.

>> Fuseki does this for TDB.  It can be used as a shared DB server.  TDB
>> is just the database engine.
>> We/Epimorphics run replicated Fusek's as well but update is not
>> instantly consistent (we don't need that for our usage).
>> If the interface in Clerezza were the SPARQL protocol, then choice of
>> the backend database is a deployment choice.
> Is there a Clerezza TcProvider that works straight on the SPARQL
> protocol? Most I have seen (TDB and Sesame) use native API's. The
> Virtuoso TcProvider mentioned by Reto almost seem to work like this, but
> is dedicated to Virtuoso and uses the jdbc route sending SPARQL requests.
>> Is there a SPARQL protocol provider?
> Currently I have no SPARQL protocol provider. I use the Clerezza
> TcProvider specifically the TDB implementation.
>>      Andy

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