No details of the "graph database" bit. Sounds like it's a graph in the sense any RDBMs is, and not with a specialised query language or helpers that any graph database gives.
Definitely wasn't meaning this post's title to be clickbait-y. The intention wasn't to hold out Spanner as a purpose-built graph database, but rather to talk about using it for a graph-y database use case. Will put together a follow-up with some more information, but in summary: * yeah, no built-ins other than relational SQL for graphs * the key thing that make this work are the ability to easily construct global indexes that aren't sharded by the primary key and reasonably fast joins between them * it's also helpful that Spanner does a reasonable job of parallelizing queries (e.g. a lot of times we'll get a 15x increase in speed vs. a sequential plan) * we then do the fan-out across the graph in our Java client
With respect, the title is wrong as that's not a graph database. "How Streak built a graph on Cloud Spanner" would be more accurate (and even then, it needs the follow-up post with some actual details).
They are building a graph database with edges and nodes, but are building it, as you said, on top of a rdbms.