The Cloud Spanner APIs now supports the request priority option.
https://cloud.google.com/blog/topics/developers-practitioners/introducing-request-priorities-cloud-spanner-apis

Are there any plans to allow the JDBC driver to specify the API request priority from the properties of the connection URL as follows?

jdbc:cloudspanner:/projects/my-project/instances/my-instance/databases/my-db;rpcPriority=LOW