Known limitations for using a PostgreSQL database as a source include:
The pglogical extension doesn't support the replication of generated columns for PostgreSQL 12+.
Changes to table structures (DDL) aren't replicated through standard DDL
commands, but only with commands executed using the pglogical
extension used for replication. This includes
changes to
enum types.
For example, pglogical provides a function
pglogical.replicate_ddl_command that allows DDL to be run on
both the source database and replica at a consistent point. The user
running this command on the source must already exist on the replica.
In order to replicate data for new tables, you must use the
pglogical.replication_set_add_table command to add
the new tables to existing replication sets.
To learn more about DDL replication while the migration is in
progress, see the section on
migration fidelity.
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.
UNLOGGED and TEMPORARY tables aren't and can't be
replicated.
Large Object data type isn't supported. More details in the section on
migration fidelity.
Database Migration Service doesn't support migrating from read replicas that are in recovery mode.
Database Migration Service doesn't support Amazon RDS sources where the AWS SCT extension pack is applied.
User-defined functions written in C can't be migrated, except for functions that are installed in the PostgreSQL database when you're installing extensions that are supported by AlloyDB.
If other extensions and procedural languages exist in the source database, or if their versions aren't supported, then when you test or start the migration job, it will fail.
Databases that are added after the migration job has started aren't migrated.
You can't select specific tables or schemas when you migrate by using Database Migration Service.
Database Migration Service migrates all tables and schemas, except for the following:
The information schema (information_schema).
Any tables that begin with pg, for example, pg_catalog. For the full list of PostgreSQL catalogs that begin with pg, see PostgreSQL system catalogs in the PostgreSQL documentation.
Information about users and user roles isn't migrated.
If encrypted databases require customer-managed encryption keys to decrypt the databases, and if Database Migration Service doesn't have access to the keys, then the databases can't be migrated.
However, if customer data is encrypted by the pgcrypto extension, then the data can be migrated with Database Migration Service (because AlloyDB supports the extension).
Database Migration Service also supports migrating data from encrypted Amazon Aurora or Amazon RDS databases because these databases handle decryption transparently in their services. For more information, see Encrypting Amazon Aurora resources and Encrypting Amazon RDS resources.
The destination AlloyDB database is
writable during the migration
to allow DDL changes to be applied if needed. Take care not to make any
changes to the database configuration or table structures which might break
the migration process or impact data integrity.
Trigger behavior depends on how they were configured. The default behavior is they
won't trigger, but if they were configured using the
ALTER EVENT TRIGGER or ALTER TABLE statement and the trigger state is set to either replica or always, then they will trigger
on the replica during replication.
Functions with security definer will be created by
alloydbexternalsync in AlloyDB primary. When it's
executed by any users, it will be executed with the privileges of
alloydbexternalsync which has alloydbsuperuser and
alloydbreplica roles. It's better to restrict use of a security
definer function to only some users. To do that, the user should revoke the
default PUBLIC privileges and then grant execute privilege selectively.
Private Service Connect interfaces connectivity method
is only supported for migrating to existing destination instances.
If you want to use private IP connectivity and migrate to a new destination
instance, use VPC peering.
Limitations for migrations to existing destination clusters
Your existing destination cluster must be empty or contain only
system configuration data. Migrating to existing destination cluster
that contain user data (such as tables) isn't supported.
You can configure only one migration job per destination cluster.
Migrating to clusters with secondary clusters isn't supported.
Migrating to clusters with read pool instances is supported.
Up to 2,000 connection profiles and 1,000 migration jobs can exist at any given
time. To create space for more, migration jobs (including completed ones)
and connection profiles can be deleted.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-25 UTC."],[[["\u003cp\u003eDatabase Migration Service supports the migration of initial snapshots and \u003ccode\u003eINSERT\u003c/code\u003e statements for tables without primary keys, but \u003ccode\u003eUPDATE\u003c/code\u003e and \u003ccode\u003eDELETE\u003c/code\u003e statements must be manually migrated.\u003c/p\u003e\n"],["\u003cp\u003eCertain PostgreSQL features are not supported during migration, including \u003ccode\u003eUNLOGGED\u003c/code\u003e and \u003ccode\u003eTEMPORARY\u003c/code\u003e tables, Large Object data types, and read replicas in recovery mode.\u003c/p\u003e\n"],["\u003cp\u003eDatabase Migration Service migrates all tables and schemas except for \u003ccode\u003einformation_schema\u003c/code\u003e and tables beginning with \u003ccode\u003epg\u003c/code\u003e, and does not migrate information about users and user roles.\u003c/p\u003e\n"],["\u003cp\u003eWhile the destination AlloyDB database remains writable during migration, modifications to the database configuration or table structures should be avoided to prevent issues.\u003c/p\u003e\n"],["\u003cp\u003eThere are quotas for the amount of migration jobs and connection profiles that can exist at any given time, set to 1,000 and 2,000 respectively, requiring deletion to create space for more.\u003c/p\u003e\n"]]],[],null,["# Known limitations\n\n\u003cbr /\u003e\n\n[MySQL](/database-migration/docs/mysql/known-limitations \"View this page for the MySQL version of Database Migration Service.\") \\| [PostgreSQL](/database-migration/docs/postgres/known-limitations \"View this page for the PostgreSQL version of Database Migration Service.\") \\| PostgreSQL to AlloyDB\n\n\u003cbr /\u003e\n\n\u003cbr /\u003e\n\n\u003cbr /\u003e\n\nKnown limitations for using a PostgreSQL database as a source include:\n\n- The `pglogical` extension doesn't support the replication of [generated columns](https://www.postgresql.org/docs/current/ddl-generated-columns.html) for PostgreSQL 12+.\n\n- Changes to table structures (DDL) aren't replicated through standard DDL\n commands, but only with commands executed using the `pglogical`\n extension used for replication. This includes\n [changes to\n `enum` types](https://www.postgresql.org/docs/current/sql-altertype.html).\n\n - For example, `pglogical` provides a function\n `pglogical.replicate_ddl_command` that allows DDL to be run on\n both the source database and replica at a consistent point. The user\n running this command on the source must already exist on the replica.\n\n - In order to replicate data for new tables, you must use the\n `pglogical.replication_set_add_table` command to add\n the new tables to existing replication sets.\n\n - To learn more about DDL replication while the migration is in\n progress, see the section on\n [migration fidelity](/database-migration/docs/postgresql-to-alloydb/migration-fidelity).\n\n- 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.\n\n- 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 `\u003cvar translate=\"no\"\u003eview_name\u003c/var\u003e.\n\n- The `SEQUENCE` states (for example, `last_value`) on the new AlloyDB destination might vary from the source `SEQUENCE` states.\n\n- `UNLOGGED` and `TEMPORARY` tables aren't and can't be\n replicated.\n\n- Large Object data type isn't supported. More details in the section on\n [migration fidelity](/database-migration/docs/postgresql-to-alloydb/migration-fidelity).\n\n\u003c!-- --\u003e\n\n- Only [extensions and procedural languages](/alloydb/docs/reference/extensions) that AlloyDB supports for PostgreSQL can be migrated.\n\n\u003c!-- --\u003e\n\n- Database Migration Service doesn't support migrating from read replicas that are in recovery mode.\n\n- Database Migration Service doesn't support Amazon RDS sources where the AWS SCT extension pack is applied.\n\n\u003c!-- --\u003e\n\n- User-defined functions written in C can't be migrated, except for functions that are installed in the PostgreSQL database when you're installing [extensions](/alloydb/docs/reference/extensions) that are supported by AlloyDB.\n\n\u003c!-- --\u003e\n\n- If other extensions and procedural languages exist in the source database, or if their versions aren't supported, then when you test or start the migration job, it will fail.\n\n- Databases that are added after the migration job has started aren't migrated.\n\n\u003c!-- --\u003e\n\n- You can't select specific tables or schemas when you migrate by using Database Migration Service. Database Migration Service migrates all tables and schemas, except for the following:\n - The information schema (`information_schema`).\n - Any tables that begin with `pg`, for example, `pg_catalog`. For the full list of PostgreSQL catalogs that begin with `pg`, see [PostgreSQL system catalogs](https://www.postgresql.org/docs/current/catalogs.html) in the PostgreSQL documentation.\n - Information about users and user roles isn't migrated.\n\n\u003c!-- --\u003e\n\n- If encrypted databases require customer-managed encryption keys to decrypt the databases, and if Database Migration Service doesn't have access to the keys, then the databases can't be migrated.\n\n However, if customer data is encrypted by the [`pgcrypto` extension](/sql/docs/postgres/extensions#miscellaneous-extensions), then the data can be migrated with Database Migration Service (because AlloyDB supports the extension).\n\n Database Migration Service also supports migrating data from encrypted Amazon Aurora or Amazon RDS databases because these databases handle decryption transparently in their services. For more information, see [Encrypting Amazon Aurora resources](https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/Overview.Encryption.html) and [Encrypting Amazon RDS resources](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Overview.Encryption.html).\n- The destination AlloyDB database is\n writable during the migration\n to allow DDL changes to be applied if needed. Take care not to make any\n changes to the database configuration or table structures which might break\n the migration process or impact data integrity.\n\n- Trigger behavior depends on how they were configured. The default behavior is they\n won't trigger, but if they were configured using the\n `ALTER EVENT TRIGGER` or `ALTER TABLE` statement and the trigger state is set to either replica or always, then they will trigger\n on the replica during replication.\n\n- Functions with security definer will be created by\n `alloydbexternalsync` in AlloyDB primary. When it's\n executed by any users, it will be executed with the privileges of\n `alloydbexternalsync` which has `alloydbsuperuser` and\n `alloydbreplica` roles. It's better to restrict use of a security\n definer function to only some users. To do that, the user should revoke the\n default PUBLIC privileges and then grant execute privilege selectively.\n\n- [Private Service Connect interfaces connectivity method](/database-migration/docs/postgresql-to-alloydb/networking-methods#psc-interfaces)\n is only supported for migrating to existing destination instances.\n If you want to use private IP connectivity and migrate to a new destination\n instance, use VPC peering.\n\n### Limitations for migrations to existing destination clusters\n\n- Your existing destination cluster must be empty or contain only system configuration data. Migrating to existing destination cluster that contain user data (such as tables) isn't supported.\n- You can configure only one migration job per destination cluster.\n- Migrating to clusters with secondary clusters isn't supported.\n- Migrating to clusters with read pool instances **is supported** .\n\n For more information on AlloyDB for PostgreSQL clusters and instances, see\n [AlloyDB for PostgreSQL overview](/alloydb/docs/overview).\n\n### Quotas\n\n- Up to 2,000 connection profiles and 1,000 migration jobs can exist at any given time. To create space for more, migration jobs (including completed ones) and connection profiles can be deleted."]]
