Real-Time Synchronization

Real-time synchronization refers to the real-time flow of key service data from sources to destinations while consistency of data can be ensured. It is different from migration. Migration means moving your overall database from one platform to another. Synchronization refers to the continuous flow of data between different services.

Supported Database Types

DRS supports real-time synchronization between databases of various types, and many-to-one synchronization.

**Table 1** Database types
Synchronization Direction	Data Flow	Source DB	Destination DB	Destination DB Type
To the cloud	MySQL->MySQL	On-premises databases Databases on an ECS Databases on other clouds RDS MySQL DB instances	RDS MySQL DB instances	Single DB instance Primary/Standby DB instance
To the cloud	PostgreSQL->PostgreSQL	On-premises databases Databases on an ECS Databases on other clouds RDS PostgreSQL DB instances	RDS PostgreSQL DB instances	Single DB instance Primary/Standby DB instance
To the cloud	DDM->MySQL	DDM	RDS MySQL DB instances	Single DB instance Primary/Standby DB instance
From the cloud	MySQL->MySQL	RDS MySQL DB instances	On-premises databases Databases on an ECS Databases on other clouds RDS MySQL DB instances	-
From the cloud	DDM->MySQL	DDM	On-premises databases Databases on an ECS	Single DB instance Primary/Standby DB instance

Synchronization Methods

DRS supports three synchronization modes: full synchronization, incremental synchronization, and full+incremental synchronization.

Full synchronization: All objects and data in non-system databases are synchronized to the destination database at a time. This mode is applicable to scenarios where service interruption is acceptable.

Incremental synchronization: Through log parsing, DRS replicates incremental data to keep sources and destinations in sync.

Full+Incremental synchronization: DRS allows you to synchronize data in real time. After a full synchronization initializes the destination database, an incremental synchronization parses logs to ensure data consistency between the source and destination databases.

**Table 2** Synchronization methods
Synchronization Direction	Data Flow	Incremental	Full	Full+Incremental	One-way/Two-way Sync
To the cloud	MySQL->MySQL	Supported	Not supported	Supported	One-way sync
To the cloud	PostgreSQL->PostgreSQL	Supported	Supported	Supported	One-way sync
To the cloud	DDM->MySQL	Not supported	Not supported	Supported	One-way sync
From the cloud	MySQL->MySQL	Supported	Not supported	Supported	One-way sync
From the cloud	DDM->MySQL	Not supported	Not supported	Supported	One-way sync

Database Versions

Data cannot be synchronized from a newer version database to an older version database.

**Table 3** Database versions
Synchronization Direction	Data Flow	Source Database Version	Destination DB Version
To the cloud	MySQL->MySQL	MySQL 5.5.x MySQL 5.6.x MySQL 5.7.x MySQL 8.0.x	MySQL 5.6.x MySQL 5.7.x MySQL 8.0.x
To the cloud	PostgreSQL->PostgreSQL	PostgreSQL 9.4.x PostgreSQL 9.5.x PostgreSQL 9.6.x PostgreSQL 10.x PostgreSQL 11.x PostgreSQL 12.x PostgreSQL Enhanced Edition PostgreSQL 13.x NOTE: If the source DB type is RDS PostgreSQL Enhanced Edition, the destination DB type must be the same.	PostgreSQL 9.5.x PostgreSQL 9.6.x PostgreSQL 10.x PostgreSQL 11.x PostgreSQL 12.x PostgreSQL Enhanced Edition PostgreSQL 13.x
To the cloud	DDM->MySQL	Based on the live network	MySQL 5.6.x MySQL 5.7.x
From the cloud	MySQL->MySQL	MySQL 5.6.x MySQL 5.7.x MySQL 8.0.x	MySQL 5.6.x MySQL 5.7.x MySQL 8.0.x
From the cloud	DDM->MySQL	Based on the live network	MySQL 5.6.x MySQL 5.7.x

Network Types

DRS supports real-time synchronization through a Virtual Private Cloud (VPC), Virtual Private Network (VPN), Direct Connect, or public network. Table 4 lists the application scenarios of each network type and required preparations.

**Table 4** Network types
Network Type	Application Scenario	Preparations
VPC	Synchronization between cloud databases	The source and destination databases must be in the same region. The source and destination databases can be in either the same VPC or in different VPCs. If source and destination databases are in the same VPC, they can communicate with each other by default. Therefore, you do not need to configure a security group. If the source and destination databases are not in the same VPC, the CIDR blocks of the source and destination databases cannot overlap each other, and the source and destination databases are connected through a VPC peering connection. The subnet CIDR blocks of the source and destination databases cannot be the same or overlap.
VPN	Synchronization from on-premises databases to cloud databases or between cloud databases across regions	Establish a VPN connection between your local data center and the VPC that hosts the destination database. Before synchronization, ensure that the VPN network is accessible.
Direct Connect	Synchronization from on-premises databases to cloud databases or between cloud databases across regions	Use a dedicated network connection to connect your data center to VPCs.
Public network	Synchronization from on-premises or external cloud databases to the destination databases.	To ensure network connectivity between the source and destination databases, perform the following operations: Enable public accessibility. Enable public accessibility for the source database based on your service requirements. Configure security group rules. Add the EIPs of the synchronization instance to the whitelist of the source database for inbound traffic. If destination databases and the synchronization instance are in the same VPC, they can communicate with each other by default. Therefore, you do not need to configure a security group. NOTE: The IP address on the Configure Source and Destination Databases page is the EIP of the synchronization instance. If SSL is not enabled, ensure that the data to be synchronized is non-confidential before synchronization.

**Table 5** Supported network types
Synchronization Direction	Data Flow	VPC	Public Network	VPN or Direct Connect
To the cloud	MySQL->MySQL	Supported	Supported	Supported
To the cloud	PostgreSQL->PostgreSQL	Supported	Supported	Supported
To the cloud	DDM->MySQL	Supported	Supported	Supported
From the cloud	MySQL->MySQL	Supported	Supported	Supported
From the cloud	DDM->MySQL	Supported	Supported	Supported

Supported Synchronization Objects

DRS allows you to synchronize different objects. The following table lists the supported objects.

**Table 6** Supported synchronization objects
Synchronization Direction	Data Flow	Table-level	Database-level	Importing an Object File
To the cloud	MySQL->MySQL	Supported	Supported	Supported
To the cloud	PostgreSQL->PostgreSQL	Supported	Supported	Supported
To the cloud	DDM->MySQL	Supported	Not supported	Not supported
From the cloud	MySQL->MySQL	Supported	Supported	Not supported
From the cloud	DDM->MySQL	Supported	Not supported	Not supported

Advanced Features

DRS supports multiple features to ensure successful data synchronization.

**Table 7** Advanced features
Feature	Description
Synchronization level	DRS supports database- and table-level synchronization. Database-level synchronization refers to a type of synchronization method using database as a unit. You do not need to select tables to be synchronized. New tables in the database are automatically added to the synchronization task. Table-level synchronization uses table as a unit, indicating that you need to add new tables to the synchronization task manually.
Mapping object names	Allows the names of synchronization objects (including databases, schemas, tables, and columns) in the source database to be different from those in the destination database. If the synchronization objects in source and destination databases have different names, you can map the source object name to the destination one. The following objects can be mapped: databases, schemas and tables.
Dynamically adding or deleting synchronization objects	During data synchronization, you can add or delete synchronization objects as required.
Conflict policy	DRS uses primary key or unique key conflict policies to ensure that tables with primary key or unique constraints in the source database can be synchronized to the destination database as expected. The following conflict policies are supported: Ignore The system will skip the conflicting data and continue the subsequent synchronization process. Overwrite Conflicting data will be overwritten. Report error The synchronization task will be stopped and fail. Ignore and overwrite: Synchronization stability is prioritized, so tasks will not be interrupted as data conflicts occur. Report error: Data quality is prioritized. Any data conflicts are not allowed, so once a conflict occurs, the synchronization task fails and an error is reported. You need to manually find the cause of the fault. If the task is in the failed state for a long time, the storage space may be used up and the task cannot be restored.
Structure synchronization	DRS does not provide data structure synchronization as an independent function during real-time synchronization. Instead, it directly synchronizes data and structures to the destination database.