Param	WithInstance Config	Description
`x-migrations-table`	`MigrationsTable`	Name of the migrations table
`x-clean-statements`	`CleanStatements`	Whether to parse and clean DDL statements before running migration towards Spanner (Required for comments and multiple statements)
`url`	`DatabaseName`	The full path to the Spanner database resource. If provided as part of `Config` it must not contain a scheme or query string to match the format `projects/{projectId}/instances/{instanceId}/databases/{databaseName}`
`projectId`		The Google Cloud Platform project id
`instanceId`		The id of the instance running Spanner
`databaseName`		The name of the Spanner database

Note: Google Cloud Spanner migrations can take a considerable amount of time. The migrations provided as part of the example take about 6 minutes to run on a small instance.
1481574547/u create_users_table (21.354507597s)
1496539702/u add_city_to_users (41.647359754s)
1496601752/u add_index_on_user_emails (2m12.155787369s)
1496602638/u create_books_table (2m30.77299181s)

DDL with comments

At the moment the GCP Spanner backed does not seem to allow for comments (See https://issuetracker.google.com/issues/159730604) so in order to be able to use migration with DDL containing comments x-clean-stamements is required

Multiple statements

In order to be able to use more than 1 DDL statement in the same migration file, the file has to be parsed and therefore the x-clean-statements flag is required

Testing

To unit test the spanner driver, SPANNER_DATABASE needs to be set. You'll need to sign-up to Google Cloud Platform (GCP) and have a running Spanner instance since it is not possible to run Google Spanner outside GCP.