From PostgreSQL to PostgreSQL¶
Supported Source and Destination Databases¶
Source DB | Destination DB |
---|---|
| RDS for PostgreSQL (9.5, 9.6, 10, 11, 12, 13, 14 and 15) Note The major version of the destination database must be the same as or later than that of the source database. |
Supported Synchronization Objects¶
Table 2 lists the objects that can be synchronized in different scenarios. DRS will automatically check the objects you selected before the synchronization.
Type | Notes |
---|---|
Objects |
|
Database Account Permission Requirements¶
To start a synchronization task, the source and destination database users must meet the requirements in the following table. Different types of synchronization tasks require different permissions. For details, see Table 3. DRS automatically checks the database account permissions in the pre-check phase and provides handling suggestions.
Type | Full | Full+Incremental |
---|---|---|
Source database user | The CONNECT permission for databases, the USAGE permission for schemas, the SELECT permission for tables, the SELECT permission for sequences, and the SELECT permission for system table catalog pg_catalog.pg_authid (used for synchronizing user passwords) | The CONNECT permission for databases, the USAGE permission for schemas, the SELECT permission for tables, the SELECT permission for sequences, the SELECT permission for system table catalog pg_catalog.pg_authid (used for synchronizing user passwords), the UPDATE, DELETE, and TRUNCATE permissions for tables that do not have primary keys, and the permission to create replication connections Note
|
Destination database user |
Note To synchronize event triggers, text search parsers, and text search templates, the destination database version must be RDS for PostgreSQL 11.11 or later, and the destination database user must be user root or a member of user root. |
Suggestions¶
Caution
When a task is being started or in the full synchronization phase, do not perform DDL operations on the source database. Otherwise, the task may be abnormal.
To keep data consistency before and after the synchronization, ensure that no data is written to the destination database during the synchronization.
The success of database synchronization depends on environment and manual operations. To ensure a smooth synchronization, perform a synchronization trial before you start the synchronization to help you detect and resolve problems in advance.
Start your synchronization task during off-peak hours. A less active database is easier to synchronize successfully. If the data is fairly static, there is less likely to be any severe performance impacts during the synchronization.
If network bandwidth is not limited, the query rate of the source database increases by about 50 MB/s during full synchronization, and two to four CPUs are occupied.
To ensure data consistency, tables to be synchronized without a primary key may be locked for 3s.
The data being synchronized may be locked by other transactions for a long period of time, resulting in read timeout.
When DRS concurrently reads data from a database, it will use about 6 to 10 sessions. The impact of the connections on services must be considered.
If you read a table, especially a large table, during the full migration, the exclusive lock on that table may be blocked.
Data-Level Comparison
To obtain accurate comparison results, start data comparison at a specified time point during off-peak hours. If it is needed, select Start at a specified time for Comparison Time. Due to slight time difference and continuous operations on data, data inconsistency may occur, reducing the reliability and validity of the comparison results.
Precautions¶
The full+incremental synchronization process consists of four phases: task startup, full synchronization, incremental synchronization, and task completion. (A single incremental synchronization task or a single full synchronization task contains three phases.) To ensure smooth synchronization, read the following notes before creating a synchronization task.
Type | Constraints |
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Starting a task |
|
Full synchronization |
|
Incremental synchronization |
|
Synchronization comparison |
|
Stopping a task |
|
Prerequisites¶
You have logged in to the DRS console.
For details about the DB types and versions supported by real-time synchronization, see Real-Time Synchronization.
You have read Suggestions and Precautions.
Procedure¶
This section uses synchronization from PostgreSQL to PostgreSQL as an example to describe how to configure a real-time synchronization task in the VPC network scenario.
On the Data Synchronization Management page, click Create Synchronization Task.
On the Create Synchronization Instance page, specify the task name, description, and the synchronization instance details, and click Next.
¶ Parameter
Description
Region
The region where the synchronization instance is deployed. You can change the region.
Project
The project corresponds to the current region and can be changed.
Task Name
The task name must start with a letter and consist of 4 to 50 characters. It can contain only letters, digits, hyphens (-), and underscores (_).
Description
The description consists of a maximum of 256 characters and cannot contain special characters
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¶ Parameter
Description
Data Flow
Select To the cloud.
Source DB Engine
Select PostgreSQL.
Destination DB Engine
Select PostgreSQL.
Network Type
Available options: VPC, Public network and VPN or Direct Connect. VPC is used as an example.
Destination DB Instance
The RDS PostgreSQL DB instance.
Synchronization Instance Subnet
Select the subnet where the synchronization instance is located. You can also click View Subnet to go to the network console to view the subnet where the instance resides.
By default, the DRS instance and the destination DB instance are in the same subnet. You need to select the subnet where the DRS instance resides and ensure that there are available IP addresses. To ensure that the synchronization instance is successfully created, only subnets with DHCP enabled are displayed.
Synchronization Mode
Full+Incremental
This synchronization mode 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.
Full
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.
Tags
This setting is optional. Adding tags helps you better identify and manage your tasks. Each task can have up to 20 tags.
After a task is created, you can view its tag details on the Tags tab. For details, see Tag Management.
Note
If a task fails to be created, DRS retains the task for three days by default. After three days, the task automatically ends.
On the Configure Source and Destination Databases page, wait until the synchronization instance is created. Then, specify source and destination database information and click Test Connection for both the source and destination databases to check whether they have been connected to the synchronization instance. After the connection tests are successful, select the check box before the agreement and click Next.
Establish the connectivity between the DRS instance and the source and destination databases.
Network connectivity: Ensure that the source and destination databases accept connections from the IP address of the DRS instance. To access databases over a public network, configure the database to accept connections from the EIP of the DRS instance. To access databases over a VPC, VPN, or Direct Connect network, configure the database to accept connections from the private IP address of the DRS instance.
Account connectivity: Ensure that the source and destination databases allows connections from the DRS instance using the username and password.
Note
The source database can be an ECS database or an RDS instance. Configure parameters based on the database type.
Scenario 1: Databases on an ECS - source database configuration
¶ Parameter
Description
Source Database Type
Select Self-built on ECS.
VPC
A dedicated virtual network in which the source database is located. It isolates networks for different services. You can select an existing VPC or create a VPC.
Subnet
A subnet provides dedicated network resources that are isolated from other networks, improving network security. The subnet must be in the AZ where the source database resides. You need to enable DHCP for creating the source database subnet.
IP Address or Domain Name
The IP address or domain name of the source database.
Port
The port of the source database. Range: 1 - 65535
Database Name
Indicates whether to specify a database. If this option is enabled, enter the database name.
Database Username
The username for accessing the source database.
Database Password
The password for the database username.
SSL Connection
SSL encrypts the connections between the source and destination databases. If SSL is enabled, upload the SSL CA root certificate.
Note
The maximum size of a single certificate file that can be uploaded is 500 KB.
If SSL is disabled, your data may be at risk.
Note
The IP address, domain name, username, and password of the source database are encrypted and stored in DRS, and will be cleared after the task is deleted.
Scenario 2: RDS DB instance - source database configuration
¶ Parameter
Description
Source Database Type
Select an RDS DB instance.
DB Instance Name
Select the RDS PostgreSQL instance to be synchronized as the source DB instance.
Database Username
The username for accessing the source database.
Database Password
The password for the database username.
¶ Parameter
Description
DB Instance Name
The RDS PostgreSQL instance you selected when creating the migration task and cannot be changed.
Database Username
The username for accessing the destination database.
Database Password
The password for the database username.
Note
The username and password of the source and destination databases are encrypted and stored in the databases and the synchronization instance during the synchronization. After the task is deleted, the username and password are permanently deleted.
On the Set Synchronization Task page, select the synchronization objects and accounts and click Next.
¶ Parameter
Description
Flow Control
You can choose whether to control the flow.
Yes
You can customize the maximum migration speed.
In addition, you can set the time range based on your service requirements. The traffic rate setting usually includes setting of a rate limiting time period and a traffic rate value. Flow can be controlled all day or during specific time ranges. The default value is All day. A maximum of three time ranges can be set, and they cannot overlap.
The flow rate must be set based on the service scenario and cannot exceed 9,999 MB/s.
No
The synchronization speed is not limited and the outbound bandwidth of the source database is maximally used, which will increase the read burden on the source database. For example, if the outbound bandwidth of the source database is 100 MB/s and 80% bandwidth is used, the I/O consumption on the source database is 80 MB/s.
Note
The flow control mode takes effect only in the full synchronization phase.
You can also change the flow control mode after creating a task. For details, see Modifying the Flow Control Mode.
Incremental Conflict Policy
The conflict policy refers to the conflict handling policy during incremental synchronization. By default, conflicts in the full synchronization phase are ignored. Select any of the following conflict policies:
Ignore
The system will skip the conflicting data and continue the subsequent synchronization process.
Report error
The synchronization task will be stopped and fail.
Overwrite
Conflicting data will be overwritten.
Synchronize
Available options: Index, Incremental DDLs, and Populate materialized views during the full synchronization phase
Populate materialized views during the full synchronization phase: This option takes effect only for materialized views that was populated in the source database. This operation affects the full synchronization performance. You perform this operation after the full synchronization is complete.
Synchronization Object
Select Tables or Databases as required.
Database-level synchronization: In full synchronization, the selected databases and the inventory data of the database objects are synchronized. In incremental synchronization, the DML and some DDL statements of all tables except unlogged tables and temporary tables are synchronized.
Table-level synchronization: In full synchronization, the inventory data of the selected tables, sequences, views, or materialized views is synchronized. In incremental synchronization, the DML and some DDL statements of the selected tables are synchronized.
If the synchronization objects in source and destination databases have different names, you can map the source object name to the destination one. For details, see Mapping Object Names.
When a schema name or table name is mapped, to prevent conflicts between indexes and constraint names, the original index name in the table is changed to the following format after synchronization: i_+hash value+original index name (which may be truncated)+_key The hash value is calculated based on the original schema name_original table name_original index name. Similarly, after the synchronization, the original constraint name on the table is changed to c_ + hash value + original constraint name (which may be truncated) + _key.
Note
To quickly select the desired database objects, you can use the search function.
If there are changes made to the source databases or objects, click in the upper right corner to update the objects to be synchronized.
If an object name contains spaces, the spaces before and after the object name are not displayed. If there are two or more consecutive spaces in the middle of the object name, only one space is displayed.
The name of the selected synchronization object cannot contain spaces.
Synchronize Account
During the synchronization, you can synchronize accounts based on your service requirements.
There are two types of accounts: accounts that can be synchronized and accounts that cannot be synchronized. For accounts that cannot be synchronized, you can view details in the Remarks column and determine whether to synchronize accounts and permissions based on your service requirements.
On the Check Task page, check the synchronization task.
If any check fails, review the cause and rectify the fault. After the fault is rectified, click Check Again.
If all check items are successful, click Next.
Note
You can proceed to the next step only when all checks are successful. If there are any items that require confirmation, view and confirm the details first before proceeding to the next step.
On the Confirm Task page, specify Start Time, confirm that the configured information is correct, and click Submit to submit the task.
¶ Parameter
Description
Started Time
Set Start Time to Start upon task creation or Start at a specified time based on site requirements.
Note
After a synchronization task is started, the performance of the source and destination databases may be affected. You are advised to start a synchronization task during off-peak hours.
After the task is submitted, you can view and manage it on the Data Synchronization Management page.
You can view the task status. For more information about task status, see Task Statuses.
You can click in the upper-right corner to view the latest task status.