From GaussDB Distributed to GaussDB Distributed¶
Supported Source and Destination Databases¶
Source DB | Destination DB |
|---|---|
|
|
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 | Constraints |
|---|---|
Synchronization scope |
|
Database User Permission Requirements¶
Before you 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.
Note
You are advised to create an independent database account for DRS task connection to prevent task failures caused by account modification.
After changing the account passwords for the source or destination databases, modify the connection information in the DRS task as soon as possible to prevent automatic retry after a task failure. Automatic retry will lock the database accounts.
Type | Full | Incremental | Full+Incremental |
|---|---|---|---|
Source database user | The user has the sysadmin role or the following minimum permissions:
| The user has the sysadmin role or the following minimum permissions:
| The user has the sysadmin role or the following minimum permissions:
|
Destination database user | The user has the sysadmin role or the following minimum permissions:
| The user has the sysadmin role or the following minimum permissions:
| The user has the sysadmin role or the following minimum permissions:
|
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 consists of four phases: task startup, full synchronization, incremental synchronization, and task completion. A single full or incremental synchronization task contains three phases. To ensure smooth synchronization, read the following notes before creating a synchronization task.
Type | Constraints |
|---|---|
Starting a task |
|
Full synchronization |
|
Incremental synchronization |
|
Data processing |
|
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¶
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.
Table 5 Task and recipient description¶ 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
!=<>'&"\Table 6 Synchronization instance settings¶ Parameter
Description
Data Flow
Select Out of the cloud.
Source DB Engine
Select GaussDB Distributed.
Destination DB Engine
Select GaussDB Distributed.
Network Type
The public network is used as an example. Available options: VPC, Public network and VPN or Direct Connect
Source DB Instance
The distributed GaussDB instance you created.
Synchronization Mode
Available options: Full+Incremental, Full, and Incremental. Full+Incremental is used as an example.
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.
Note
If you select Full+Incremental, data generated during the full synchronization will be continuously synchronized to the destination database, and the source remains accessible.
Full
In this mode, data is synchronized from the source to the destination at a time.
Incremental
Through log parsing, incremental data generated on the source database is synchronized to the destination database.
Specifications
DRS instance specifications. Different specifications have different performance upper limits. For details, see Real-Time Synchronization.
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, 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 DRS instance.
Account connectivity: Ensure that the source and destination databases allows connections from the DRS instance using the username and password.
Table 7 Source database settings¶ Parameter
Description
DB Instance Name
The distributed GaussDB instance selected during synchronization task creation. This parameter cannot be changed.
Database Username
The username for accessing the source database.
Database Password
The password for the database username.
Note
The username and password of the source database are encrypted and stored in the database and the synchronization instance during the synchronization. After the task is deleted, the username and password are permanently deleted.
Table 8 Destination database settings¶ Parameter
Description
IP Address or Domain Name
IP address or domain name of the destination database in the IP address/Domain name:Port format. The port of the destination database. Range: 1 - 65535
You can enter up to 10 groups of IP addresses or domain names of the source database. Separate multiple values with commas (,). For example: 192.168.0.1:8080,192.168.0.2:8080.
Database Username
The username for accessing the destination database.
Database Password
The password for the database username.
Note
The username and password of the destination database are encrypted and stored in the database 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 policy and synchronization objects, and click Next.
Table 9 Synchronization Object¶ 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.
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.
Synchronization Object
Select Tables or Import object file based on your service requirements.
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 Changing Object Names (Mapping Object Names).
When you map a schema name or table name to the target object, name the indexes and constraints of the mapped table in the following format: prefix + full name-based hash value + original index/constraint name + _key to prevent index/constraint name conflicts. The prefix of the index is
i_, the prefix of the constraint isc_, and the full name is "schema name_table name_index/constraint name". The original index/constraint name may be truncated due to length limitation.You can change object names when you select Import object file. For details, see Importing Synchronization Objects.
Note
You can search for table names to quickly select the required database objects.
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.
On the Advanced Settings page, set the parameters for full+incremental synchronization selected in 2 and click Next.
Table 10 Full synchronization settings¶ Parameter
Description
Default Value
Synchronization Object Type
Select whether to synchronize indexes based on the service requirements. Table structure and data are mandatory.
All options
Concurrent Export Tasks
Number of export threads. Value range: 1 to 16. A larger value indicates higher load on the source database.
8
Concurrent Import Tasks
Number of import threads. Value range: 1 to 16. A larger value indicates higher load on the destination database.
8
Rows per Shard
Value range: 0 or 520,000 to 1,000,000,000
0
All tables are not sharded, and each table is synchronized as a whole.
Other values
The table is sharded based on the specified value (or the primary key column). If the number of records in a table is less than the value of this parameter, the table is not sharded.
520000
Table 11 Incremental synchronization settings¶ Parameter
Description
Default Value
Concurrent Replay Tasks
Number of concurrent threads for data replay. Value range: 1 to 64. Incremental data is concurrently written to the destination database. A larger value indicates higher load on the destination database.
64
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.
Table 12 Task startup settings¶ 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.By default, DRS retains a task in the Configuration state for three days. After three days, DRS automatically deletes background resources, but the task status remains unchanged. When you reconfigure the task, DRS applies for resources for the task again.