POC migrations
Spanner migration tool can two POC migrations in two ways:
Dump Files
Native dump files are only supported for MySQL and PostgreSQL. CSVs are also supported, which are source-agnostic.
Spanner migration tool can accept MySQL and PostgreSQL dump files, parse them, generate a Spanner compatible schema for it and then migrate the schema/data/schema-and-data to the Spanner database.
Direct connection to source database
Spanner migration tool (SMT) reads data from source database and writes it to the database created in Cloud Spanner. Changes which happen to the source database during the POC migration may or may not be written to Spanner. To achieve consistent version of data, stop writes on the source while migration is in progress, or use a read replica. Performing schema changes on the source database during the migration is not supported. While there is no technical limit on the size of the database, it is recommended for migrating moderate-size datasets to Spanner(up to about 100GB).