You can use Data Transmission Service (DTS) to migrate incremental data between PostgreSQL databases. The source or destination database can be a self-managed PostgreSQL database or an ApsaraDB RDS for PostgreSQL instance. DTS supports schema migration, full data migration, and incremental data migration. You can create a task that includes all three migration types to ensure service continuity. This topic describes how to migrate incremental data from a self-managed PostgreSQL database to an ApsaraDB RDS for PostgreSQL instance.
Prerequisites
- The self-managed PostgreSQL database is of a version from 10.1 to 13.0.
- An ApsaraDB RDS for PostgreSQL instance is created. For more information, see Create an ApsaraDB RDS for PostgreSQL instance.
Note To ensure compatibility, you must make sure that the database version of the ApsaraDB RDS for PostgreSQL instance is the same as the version of the self-managed PostgreSQL database.
- The available storage space of the ApsaraDB RDS for PostgreSQL instance is larger than the total size of the data in the self-managed PostgreSQL database.
Precautions
- DTS uses read and write resources of the source and destination databases during full data migration. This may increase the loads of the database servers. If the database performance is unfavorable, the specification is low, or the data volume is large, database services may become unavailable. For example, DTS occupies a large amount of read and write resources in the following cases: a large number of slow SQL queries are performed on the source database, the tables have no primary keys, or a deadlock occurs in the destination database. Before you migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. For example, you can migrate data when the CPU utilization of the source and destination databases is less than 30%.
- The tables to be migrated in the source database must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records.
- During incremental data migration, if you select a schema to migrate, take note of
the following requirements: If you create a table in the schema or run the RENAME
command to rename a table in the schema, you must run the
ALTER TABLE schema.table REPLICA IDENTITY FULL;
command before you write data to the table.Note Replace theschema
andtable
in the preceding sample command with the actual schema name and table name. - To ensure that the accurate delay time of incremental data migration is displayed, DTS adds a heartbeat table named dts_postgres_heartbeat to the source database.
- During incremental data migration, DTS creates a replication slot in the source database.
The replication slot is prefixed with
dts_sync_
. DTS automatically clears historical replication slots every 90 minutes to reduce storage usage.Note If the data migration task is released or fails, DTS automatically clears the replication slot. If a primary/secondary switchover is performed on the ApsaraDB RDS for PostgreSQL instance, you must log on to the secondary database to clear the replication slot manually. - To ensure that the data migration task runs as expected, you can perform a primary/secondary
switchover only on a V11 ApsaraDB RDS for PostgreSQL instance. In this case, you must
set the
rds_failover_slot_mode
parameter tosync
. For more information, see Logical Replication Slot Failover.Warning If you perform a primary/secondary switchover on a self-managed PostgreSQL database or an ApsaraDB RDS for PostgreSQL instance of a version other than V11, the data migration task stops. - If a data migration task fails, DTS automatically resumes the task. Before you switch your workloads to the destination instance, stop or release the data migration task. Otherwise, the data in the source database will overwrite the data in the destination instance after the task is resumed.
Limits
- A single data migration task can migrate data from only one database. To migrate data from multiple databases, you must create a data migration task for each source database.
- The name of the source database cannot contain hyphens (-), for example, dts-testdata.
- If a primary/secondary switchover is performed on the source database during incremental data migration, the transmission cannot be resumed.
- Data may be inconsistent between the primary and secondary nodes of the source database
due to synchronization delay. Therefore, you must use the primary node as the data
source when you migrate data.
Note We recommend that you migrate data during off-peak hours. You can modify the transfer rate of full data migration based on the read/write performance of the source database. For more information, see Modify the transfer rate of full data migration.
- Incremental data migration does not support the BIT data type.
- During incremental data migration, DTS migrates only data manipulation language (DML)
operations. DML operations include INSERT, DELETE, and UPDATE.
Note Only data migration tasks that are created after October 1, 2020 can migrate data definition language (DDL) operations. You must create a trigger and function in the source database to obtain the DDL information before you configure the task. For more information, see Use triggers and functions to implement incremental DDL migration for PostgreSQL databases.
- After your workloads are switched to the destination database, newly written sequences do not increment from the maximum value of the sequences in the source database. Therefore, you must query the maximum value of the sequences in the source database before you switch your workloads to the destination database. Then, you must specify the queried maximum value as the starting value of the sequences in the destination database.
- DTS does not check the validity of metadata such as sequences. You must manually check the validity of metadata.
Billing
Migration type | Task configuration fee | Internet traffic fee |
---|---|---|
Schema migration and full data migration | Free of charge. | Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Pricing. |
Incremental data migration | Charged. For more information, see Pricing. |
Permissions required for database accounts
Database | Schema migration | Full data migration | Incremental data migration |
---|---|---|---|
Self-managed PostgreSQL database | The USAGE permission on pg_catalog | The SELECT permission on the objects to be migrated | The permissions of the superuser role |
ApsaraDB RDS for PostgreSQL instance | The CREATE and USAGE permissions on the objects to be migrated | The permissions of the schema owner | The permissions of the schema owner |
For more information about how to create a database account and grant permissions to the account, see the following topics:
- Self-managed PostgreSQL database: CREATE USER and GRANT
- ApsaraDB RDS for PostgreSQL instance: Create an account on an ApsaraDB RDS for PPAS instance.
Data migration process
The following table describes how DTS migrates the schemas and data of the source PostgreSQL database. The process prevents data migration failures that are caused by dependencies between objects.
Data migration process | Description |
---|---|
1. Schema migration | DTS migrates the schemas of tables, views, sequences, functions, user-defined types,
rules, domains, operations, and aggregates to the destination database.
Note DTS does not migrate plug-ins. In addition, DTS does not migrate functions that are
written in the C programming language.
|
2. Full data migration | DTS migrates all historical data of the required objects to the destination database. |
3. Schema migration | DTS migrates the schemas of triggers and foreign keys to the destination database. |
4. Incremental data migration | DTS migrates incremental data of the required objects to the destination database.
Incremental data migration ensures service continuity of self-managed applications.
Note
|
Preparation
Procedure
Stop the migration task
- Full data migration
Do not manually stop a task during full data migration. Otherwise, the system may fail to migrate all data. Wait until the migration task automatically ends.
- Incremental data migration
The task does not automatically end during incremental data migration. You must manually stop the migration task.
- Wait until the task progress bar shows Incremental Data Migration and The migration task is not delayed. Then, stop writing data to the source database for a few minutes. In some cases, the progress bar shows the delay time of incremental data migration.
- After the status of incremental data migration changes to The migration task is not delayed, manually stop the migration task.