Another point is that since all records are globally timestamped, you can do a read that is consistent at a timestamp in the past (i.e. read data as the database was 1 second ago, or something like that).
If data from other places has synchronized to your zone, you may be able to do this globally-consistent read while only touching your local datacenter (because TrueTime guarantees that no other records anywhere in the system will be created at the time you are querying).
Note: I work at Google, but I don't know more about Spanner than the Spanner paper.
If data from other places has synchronized to your zone, you may be able to do this globally-consistent read while only touching your local datacenter (because TrueTime guarantees that no other records anywhere in the system will be created at the time you are querying).
Note: I work at Google, but I don't know more about Spanner than the Spanner paper.