There is no ready-made bulk loading tool available for Sesame that I am aware of - though Sesame-compatible triplestore vendors do have such tooling available as part of their specific database. Programming a bulk-upload solution is not particularly hard, but we somehow never got around to including such a tool...
Your code creates a new repository (by adding a new repository configuration to the repository manager) every time you execute the connectToRepository() method. Since you use the exact same repository configuration (including the actual id of the repository) every time, naturally this causes an error the second time you execute...
concurrency,transactions,sparql,sesame,openrdf
Sesame currently supports no transaction isolation over HTTP. In a HTTP connection, transactions merely batch operations together at the client side, but no lock is obtained from the server, so there is no way to control isolation in this scenario. So the only way to deal with this, really, is...
xml,sparql,sesame,dotnetrdf,openrdf
The extra attribute q:qname is a Sesame-specific extension of the standard format. It is a configuration setting that is supported by Sesame's SPARQLXMLWriter but is not enabled by default. It appears, however, that the Workbench client application enables this feature and adds these additional attributes when exporting query results. So...