Help Center/ Data Replication Service/ Real-Time Synchronization/ To the Cloud/ From Cassandra to GeminiDB Cassandra

Updated on 2024-09-25 GMT+08:00

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From Cassandra to GeminiDB Cassandra

Supported Source and Destination Databases

**Table 1** Supported databases
Source DB	Destination DB
On-premises Cassandra databases ECS-hosted Cassandra databases	GeminiDB Cassandra instances

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.

**Table 2** Supported synchronization objects
Type	Synchronization Scope
Synchronization scope	Supported scenario: Full synchronization Supported fields: ASCII, BIGINT, BLOB, BOOLEAN, COUNTER, DATE, DECIMAL, DOUBLE, DURATION, FLOAT, INET, INT, LIST, MAP, SET, SMALLINT, TEXT, TIME, TIMESTAMP, TIMEUUID, TINYINT, UUID, VARCHAR and VARINT. Table-level synchronization or object file import is supported. During full synchronization, only table data and table structures can be synchronized. Table-level and column-level TTLs cannot be synchronized. Tables containing fields of the FROZEN, TUPLE, and USER-DEFINED types cannot be synchronized. If you select tables by importing an object file, ensure that the imported table exists in the source database or is visible to the synchronization user. If you select synchronization objects by importing an object file, the token of a table cannot be specified. The default value 12 is used.

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.

You are advised to create an independent database account for DRS task connection to prevent task failures caused by database account password modification.
After changing the account passwords for the source and destination databases, modify the connection information of the DRS task by referring to Modifying Connection Information to prevent automatic retry after a task failure. Automatic retry will lock the database accounts.

**Table 3** Database user permissions
Type	Full Synchronization
Source database user	The user must have the following minimum permissions: SELECT permission on system catalogs system_auth.roles and system_auth.role_permissions and on the tables to be synchronized.
Destination database user	The user must have the following permissions: SELECT permission on system catalogs system_auth.roles and system_auth.role_permissions and CREATE permission on keyspaces. If the table to be synchronized already exists in the destination database, the SELECT and MODIFY permissions on the table are required.

Suggestions

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.
You are advised to start your synchronization task during off-peak hours by setting Start Time to Start at a specified time. 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.
- 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 synchronization, the exclusive lock on that table may be blocked.
- For more information about the impact of DRS on databases, see How Does DRS Affect the Source and Destination Databases?

Precautions

DRS full synchronization consists of three phases: task start, full synchronization, and task completion. To ensure smooth synchronization, read the following notes before creating a synchronization task.

**Table 4** Precautions
Type	Restrictions
Starting a task	The primary data center can be configured. You can enter a data center name. This configuration affects the load balancing policy and consistency level for data read from the source database. You can run the following command to query a data center name: select data_center from system.local; or select data_center from system.peers; The default load balancing policy for data read is RoundRobinPolicy. When a primary data center is configured, the policy is DCAwareRoundRobinPolicy. If this configuration is incorrect, data may fail to be read. The default consistency level for data read is EACH_QUORUM. In earlier versions (2.0 and 2.1), the level is ALL. When a primary data center is configured, the level is LOCAL_QUORUM. The number of table tokens can be set during synchronization. The Z01_TABLE_TOKENS attribute can be specified when a table is created.
Full synchronization	Do not change the port of the source and destination databases, or change or delete the passwords and permissions of the source and destination database users. Otherwise, the task may fail. Do not execute any DDL statement in the source database. Otherwise, data may be inconsistent or the task may fail. Do not write data to the destination database. Otherwise, data may be inconsistent. To ensure normal synchronization and data consistency, you are advised to create a DRS task again during off-peak hours to meet the preceding requirements.

Procedure

This section uses real-time synchronization from Cassandra to GeminiDB Cassandra as an example to describe how to configure a real-time synchronization task.

On the Data Synchronization Management page, click Create Synchronization Task.

On the Create Synchronization Instance page, select a region and project, specify the task name, description, and the synchronization instance details, and click Create Now.

Task information description

Figure 1 Synchronization task information

**Table 5** Task information
Parameter	Description
Region	The region where the replication 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 !=<>'&"\

Synchronization instance information

Figure 2 Synchronization instance information

**Table 6** Synchronization instance settings
Parameter	Description
Data Flow	Select To the cloud.
Source DB Engine	Select Cassandra.
Destination DB Engine	Select GeminiDB Cassandra.
Network Type	Public network is used as an example. Available options: VPC, Public network, and VPN or Direct Connect VPC is suitable for data synchronization between cloud databases of the same account in the same region and VPC. Public network is suitable for data synchronization from on-premises or external cloud databases to the destination databases bound with an EIP. VPN or Direct Connect is suitable for data synchronization from on-premises databases to cloud databases, between databases of different accounts in the same region on the cloud, or between databases across regions on the cloud using a VPN, Direct Connect, Cloud Connect, VPCEP, or a VPC peering connection.
Destination DB Instance	Select an available GeminiDB Cassandra instance.
Synchronization Instance Subnet	Select the subnet where the synchronization instance is located. You can also click View Subnets 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 there are available IP addresses for the subnet. To ensure that the synchronization instance is successfully created, only subnets with DHCP enabled are displayed.
Synchronization Mode	The synchronization mode supported by a DRS task. For details about the underlying working principles for full or incremental synchronization, see Product Architecture and Function Principles. Full: All database objects and data you selected are synchronized to the destination database at a time. This mode is applicable to scenarios where service interruption is acceptable.
Specify EIP	This parameter is available when you select Public network for Network Type. Select an EIP to be bound to the DRS instance. DRS will automatically bind the specified EIP to the DRS instance and unbind the EIP after the task is complete. The number of specified EIPs must be the consistent with that of DB instances. For details about the data transfer fee generated using a public network, see EIP Price Calculator.

Figure 3 AZ

**Table 7** Task AZ
Parameter	Description
AZ	Select the AZ where you want to create the DRS task. Selecting the one housing the source or destination database can provide better performance.

Enterprise Project and Tags

Figure 4 Enterprise projects and tags

**Table 8** Enterprise Project and Tags
Parameter	Description
Enterprise Project	An enterprise project you would like to use to centrally manage your cloud resources and members. Select an enterprise project from the drop-down list. The default project is default. For more information about enterprise project, see Enterprise Management User Guide. To customize an enterprise project, click Enterprise in the upper right corner of the console. The Enterprise Project Management Service page is displayed. For details, see Creating an Enterprise Project in Enterprise Management User Guide.
Tags	Tags a task. This configuration is optional. Adding tags helps you better identify and manage your tasks. Each task can have up to 20 tags. If your organization has configured tag policies for DRS, add tags to tasks based on the policies. If a tag does not comply with the policies, task creation may fail. Contact your organization administrator to learn more about tag policies. After a task is created, you can view its tag details on the Tags tab. For details, see Tag Management.

If a task fails to be created, DRS retains the task for three days by default. After three days, the task automatically stops.

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.

Figure 5 Source database information

**Table 9** Source database settings
Parameter	Description
IP Address or Domain Name	The IP address or domain name of the source database.
Database Username	The username for accessing the source database.
Database Password	The password for the database username.

The username and password of the source database are encrypted and stored in DRS and will be cleared after the task is deleted.

Figure 6 Destination database information

**Table 10** Destination database settings
Parameter	Description
DB Instance Name	The GeminiDB Cassandra instance selected when you created the synchronization task. This parameter cannot be changed.
Database Username	The username for accessing the destination database.
Database Password	The password for the database username. The database username and password are encrypted and stored in the system, and will be cleared after the task is deleted.

On the Set Synchronization Task page, select the synchronization object type and synchronization objects, and click Next.

Figure 7 Synchronization mode

**Table 11** Synchronization mode and object
Parameter	Description
Flow Control	You can choose whether to control the flow. Flow Control takes effect in the full phase only. Yes You can customize the maximum synchronization speed. During the full synchronization, the synchronization speed of each task (or each subtask in multi-task mode) does not exceed the value of this parameter. 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 Always. 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. Figure 8 Flow control 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.
Active Data Center Name	Enter a data center name. This configuration affects the load balancing policy and consistency level for data read from the source database. You can run the following command to query a data center name: select data_center from system.local; or select data_center from system.peers;
Synchronization Object	The left pane displays the source database objects, and the right pane displays the selected objects. You can select Tables or Import object file based on your service requirements. On the right pane, you can set tokens for selected objects in batches. 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). A mapped table name can contain 1 to 48 characters. Only letters, digits, and underscores (_) are allowed. For details about how to import an object file, see Importing Synchronization Objects. 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.

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.
  For details about how to handle check failures, see Solutions to Failed Check Items in Data Replication Service User Guide.
- If all check items are successful, click Next.
  
  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 displayed page, specify Start Time, Send Notifications, SMN Topic, Delay Threshold (s), and Stop Abnormal Tasks After, confirm that the configured information is correct, select the check box before the agreement, and click Submit to submit the task.

Figure 9 Task startup settings

**Table 12** Task startup settings
Parameter	Description
Start 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.
Send Notifications	This parameter is optional. After enabled, select a SMN topic. If the status, latency metric, or data of the migration task is abnormal, DRS will send you a notification.
SMN Topic	This parameter is available only after you enable Send Notifications and create a topic on the SMN console and add a subscriber. For details, see Simple Message Notification User Guide.
Delay Threshold (s)	During an incremental synchronization, a synchronization delay indicates a time difference (in seconds) of synchronization between the source and destination database. If the synchronization delay exceeds the threshold you specify, DRS will send alarms to the specified recipients. The value ranges from 0 to 3,600. To avoid repeated alarms caused by the fluctuation of delay, an alarm is sent only after the delay has exceeded the threshold for six minutes. NOTE: If the delay threshold is set to 0, no notifications will be sent to the recipient. In the early stages of an incremental synchronization, the synchronization delay is long because a large quantity of data is awaiting synchronization. In this case, no notifications will be sent. Before setting the delay threshold, enable Send Notifications.
Data Exception Notification	This parameter is optional. After enabled, DRS will send a notification if the task data is abnormal.
Stop Abnormal Tasks After	Number of days after which an abnormal task is automatically stopped. The value must range from 14 to 100. The default value is 14. NOTE: You can set this parameter only for pay-per-use tasks. Tasks in the abnormal state are still charged. If tasks remain in the abnormal state for a long time, they cannot be resumed. Abnormal tasks run longer than the period you set (unit: day) will automatically stop to avoid unnecessary fees.

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 configure the task again, DRS applies for resources for the task again. In this case, the IP address of the DRS instance changes.
- For a public network task, DRS needs to delete background resources after you stop the task. The EIP bound to the task cannot be restored to the Unbound state until background resources are deleted.