This "modern" Spanner feels very different from the one we saw in 2012 [1]. Some interesting takeaways:
* There is a native SQL interface in Spanner, rather than relying on a separate upper-layer SQL layer, a la F1 [2]
* Spanner is no longer on top of Bigtable! Instead, the storage engine seems to be a heavily modified Bigtable with a column-oriented file format
* Data is resharded frequently and concurrently with other operations -- the shard layout is abstracted away from the query plan using the "distributed union" operator
* Possible explanation for why Spanner doesn't support SQL DML writes: writes are required to be the last step of a transaction, and there is currently no support for reading uncommitted writes (this is in contrast to F1, which does support DML)
* Spanner supports full-text search (!)