I would to suggest increase the length of debug string by 4 values (to fill dashes).
Spanner does not have the sequence structure and doesn't manage sequence-table, so as primary key uuid is chosen very often.

In debug mode it's would be better to use toString() of statements values and display uuid in full.
According to https://tools.ietf.org/html/rfc4122#section-3 uuid has (32 hex + 4 dashes) characters.