It's variable, and the client can provide it. By default, we use the greater of wall clock time or the highest timestamp transaction timestamp the node serving the query has seen.
To be clear, read-write transactions are applied in a consistent order derived from the transaction log. Read-only transactions can rely on the fact that read-write transactions are totally ordered, and execute without global coordination while still providing a guarantee of serializability. Wall clock time is used as a suggestion only, in order for the database's logical timestamps to track as close to real time as possible.
We will have more information about how Fauna meets its consistency guarantees in a future blog post.
you can't have a read transaction that's serializable that doesn't go through global coordination unless all of the data is guaranteed to only ever be local. Looking forward to the blog post.
