I stumbled upon a Wikidata Scalability blog post by Magnus Manske (cc'd
in on this message)  that contains the following excerpt:
"One of theproposed alternatives
blazegraph is Virtuoso. It models the graph structure of Wikidata in
MySQL. Even before I read about that, I had a similar thought. But
unlike Virtuoso, which is a general solution, Wikidata is a special
case, with optimization potential. So I went to do a bit of tinkering.
The following was done in the last few days, so it’s not exactly pretty,
but initial results are promising."
That's incorrect. Virtuoso is a multi-model DBMS with its own SQL and
RDF engines that have nothing to do with MySQL.
Uniprot hosts 100 Billion+ triples, accessed 24/7 globally, handling
unpredictable query complexity and solution size unpredictability using
a single-server instance of the open source edition of Virtuoso. The
same applies to a vast majority of nodes in the massive LOD Cloud.
Scalability has never been a Virtuoso issue since the very inception of
the LOD Cloud bootstrapped by DBpedia (yet another Virtuoso instance).
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