Database Migration Service for AlloyDB FAQ

• Amazon RDS 9.6.10+, 10.5+, 11.1+, 12, 13, 14, 15
• Amazon Aurora 10.11+, 11.6+, 12.4+, 13.3+, 14, 15
• Self-managed PostgreSQL (on premises or on any cloud VM that you fully control) 9.4, 9.5, 9.6, 10, 11, 12, 13, 14, 15
• Cloud SQL 9.6, 10, 11, 12, 13, 14, 15

• AlloyDB for PostgreSQL 14, 15, 16

• All schemas and all tables from the selected database.

• Naming
• Primary key
• Data type
• Ordinal position
• Default value
• Nullability
• Auto-increment attributes
• Secondary indexes

• Stored Procedures
• Functions
• Triggers
• Views
• Foreign key constraints

1. Stop writes to the source and run the DDL commands in both the source and the destination. Before running DDL commands on the destination, grant the alloydbexternalsync role to the Cloud SQL user applying the DDL changes. To enable querying or changing the data, grant the alloydbexternalsync role to the relevant Cloud SQL users.

2. Use the pglogical.replicate_ddl_command to run DDL on the source and destination at a consistent point. The user running this command must have the same username on both the source and the destination, and should be the superuser or the owner of the artifact being migrated (for example, the table, sequence, view, or database).

   Here are a few examples of using the pglogical.replicate_ddl_command.

   To add a column to a database table, run the following command:

   select pglogical.replicate_ddl_command('ALTER TABLE [schema].[table] add column surname varchar(20)', '{default}');

   To change the name of a database table, run the following command:

   select pglogical.replicate_ddl_command('ALTER TABLE [schema].[table] RENAME TO [table_name]','{default}');

   To create a database table, run the following commands:

   1. select pglogical.replicate_ddl_command(command := 'CREATE TABLE [schema].[table] (id INTEGER PRIMARY KEY, name VARCHAR);', replication_sets := ARRAY['default'']);
   2. select pglogical.replication_set_add_table('default', '[schema].[table]');

To add users to the AlloyDB destination instance, add them from the PostgreSQL client. Learn more about creating and managing PostgreSQL users.

Large objects can't be replicated because PostgreSQL's logical decoding facility doesn't support decoding changes to large objects. For tables that have column type oid referencing large objects, the rows are still synced, and new rows are replicated. However, trying to access the large object on the destination database (read using lo_get, export using lo_export, or check the catalog pg_largeobject for the given oid), fails with a message saying that the large object doesn't exist.

For tables that don't have primary keys, Database Migration Service supports migration of the initial snapshot and INSERT statements during the change data capture (CDC) phase. You should migrate UPDATE and DELETE statements manually.

Database Migration Service doesn't migrate data from materialized views, just the view schema. To populate the views, run the following command: REFRESH MATERIALIZED VIEW view_name.

The SEQUENCE states (for example, last_value) on the new AlloyDB destination might vary from the source SEQUENCE states.