Re Wikidata, it's worth noting that they discarded TitanDB because it was assumed dead after the Datastax acquisition of Aurelius, which turned out not to be the case after all.
Also, the choice of BlazeGraph whiffed of politics. Wikidata (or at least one of the primary developers) seems to have been courted by the BlazeGraph people, to the point where Wikidata prematurely abandoned their research spreadsheet. This was at a time when there was hardly any public info/documentation about BlazeGraph, and its pedigree seemed completely unknown/untested.
BlazeGraph seems like a reasonable product (now). But I don't like seeing this "Wikidata evaluated products and chose Blazegraph" thing - they started an evaluation process.
AFAICT, Titan is effectively dead, being replaced by Datastax Graph. Likewise, Blazegraph is about graph computation (think Spark's GraphX, OLAP) rather than simple reads/writes (OLTP). Systems can try to straddle both, but the benchmarks should be different.
Quickly looking at this project suggests it's on the OLTP side, not OLAP, so apples/oranges. Claiming more performance than a GPU compute engine would need some real benchmarking ;-)
Blazegraph is about graph computation (think Spark's GraphX, OLAP)
This is definitely incorrect. Wikidata uses it exclusively for read/write queries.
The (GPU accelerated) graph processing in BlazeGraph is new, and it's pretty unclear to me if it actually does the (GraphX) style processing. The examples[1] are all query-based.
Blazegraph has multiple backends. Their GPU compute engine vs. their classic DB engine are different ones. And yes, I doubt they use the same approach as GraphX, considering they've published how they don't (MapGraph) and GPUs require way more work. Lumping all these systems together doesn't make sense: reads aren't writes, and there's a whole world of graph computations. Benchmarks matter.
That said, I'd be skeptical of a GPU system for being great at writes, and I'd be skeptical of a non-GPU one computing better than one on GPUs.
There's quite a lot of activity on http://github.com/thinkaurelius/titan for a dead project. Admittedly, the issues are piling up, but the code seems to be actively worked on.
Also, the choice of BlazeGraph whiffed of politics. Wikidata (or at least one of the primary developers) seems to have been courted by the BlazeGraph people, to the point where Wikidata prematurely abandoned their research spreadsheet. This was at a time when there was hardly any public info/documentation about BlazeGraph, and its pedigree seemed completely unknown/untested.