From GaussDB Primary/Standby to MySQL_Data Replication Service

Supported Source and Destination Databases

**Table 1** Supported databases
Source DB	Destination DB
GaussDB primary/standby	On-premises MySQL 5.5, 5.6, and 5.7 databases ECS-hosted MySQL 5.5, 5.6, and 5.7 databases MySQL 5.5, 5.6, and 5.7 databases on other clouds

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	Instance-level synchronization is not supported. Only one database can be synchronized at a time. To synchronize multiple databases, create multiple tasks. Supported scenarios: full synchronization, incremental synchronization, and full+incremental synchronization. Supported fields: INTEGER, TINYINT, SMALLINT, BIGINT, TINYINT UNSIGNED, SMALLINT UNSIGNED, INTEGER UNSIGNED, BIGINT UNSIGNED, NUMBER, NUMERIC, REAL, DOUBLE PRECISION, CHARACTER, CHARACTER VARYING, NVARCHAR2, BIT, BIT VARYING, BLOB, BYTEA, CLOB, RAW, TEXT, BOOLEAN, DATE, SMALLDATETIME, TIME WITH TIME ZONE, TIME WITHOUT TIME ZONE, TIMESTAMP WITH TIME ZONE, TIMESTAMP WITHOUT TIME ZONE, and MONEY Table-level synchronization is supported. During full synchronization, only data in the selected tables can be synchronized. During incremental synchronization, only DML statements of selected tables can be synchronized. Databases without schemas cannot be synchronized. Schemas without tables cannot be synchronized. Column-store tables, compressed tables, delay tables, temporary tables, and tables containing generated columns cannot be synchronized. Do not synchronize unlogged tables in the incremental phase. System schemas (pg_toast, cstore, snapshot, sys, dbms_job, dbms_perf, pg_catalog, information_schema, utl_file, dbms_output, dbms_random, utl_raw, dbms_sql, dbms_lob, dbe_perf, pkg_service, pkg_util, dbe_file, dbe_random, dbe_output, dbe_raw, dbe_sql, dbe_lob, dbe_task, blockchain, db4ai, dbe_pldebugger, sqladvisor, dbe_application_info, dbe_match, dbe_pldeveloper, dbe_scheduler, dbe_session, dbe_utility, dbe_sql_util, dbe_xml, dbe_xmldom, dbe_xmlparser, dbe_compression, dbe_heat_map, dbe_ilm, dbe_ilm_admin, prvt_ilm, dbe_profiler, dbe_stats, rdsBackup, rdsMetric, rdsRepl and public) cannot be synchronized. System tables (redis_progress_detail, redis_status, pgxc_redsitb and redis_progress in the public schema) cannot be synchronized. The database name, schema name, and table name cannot contain special characters /<.>\\'`\|\?! The column name cannot contain double quotation marks ("), single quotation marks ('), or periods (.).

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 permission
Type	Full	Incremental	Full+Incremental
Source database user	The user has the sysadmin role or the following minimum permissions: The CONNECT permission for databases, USAGE permission for schemas, SELECT or UPDATE permission for tables, the UPDATE permission for locking tables without primary keys, and SELECT permission for sequences. The user must have the remote connection permission. For details about how to assign the remote connection permission to a database user, see Configuring Remote Connection to a GaussDB Database.	The user has the sysadmin role or the following minimum permissions: The REPLICATION permission or the permission inherited from the built-in role gs_role_replication, the CONNECT permission for databases, the USAGE permission for schemas, and the SELECT permission for tables. The user must have the remote connection permission. For details about how to assign the remote connection permission to a database user, see Configuring Remote Connection to a GaussDB Database. Ensure that the connection ports are enabled in the security group and firewall policies. For details, see Connection and Port Description for Incremental Synchronization from GaussDB.	The user has the sysadmin role or the following minimum permissions: The REPLICATION permission or the permission inherited from the built-in role gs_role_replication, the CONNECT permission for databases, the USAGE permission for schemas, the SELECT or UPDATE permission for tables, the UPDATE permission for locking tables that do not have primary keys, and the SELECT permission for sequences. The user must have the remote connection permission. For details about how to assign the remote connection permission to a database user, see Configuring Remote Connection to a GaussDB Database. Ensure that the connection ports are enabled in the security group and firewall policies. For details, see Connection and Port Description for Incremental Synchronization from GaussDB.
Destination database user	Required permissions: INSERT, DELETE, UPDATE, SELECT, and SHOW DATABASES

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.

**Table 4** Precautions
Type	Restrictions
Starting a task	Source database parameter requirements: If incremental synchronization or full+incremental synchronization is selected: The wal_level parameter of the source database is set to logical. The enable_slot_log parameter of the source database is set to on. The max_replication_slots value of the source database must be greater than the number of used replication slots. Add a primary key to the table that does not have a primary key, or set REPLICA IDENTITY to FULL for the table that does not have a primary key. Source database object requirements: The names of the source database, schema, and table to be synchronized cannot contain special characters /<.>\\'`\|\?! The destination database parameters must meet the following requirements: The destination database has sufficient disk space. The source database supports the UTF8 character set, and the destination database supports the UTF8MB4 character set. If the source database uses the UTF8 character set and the destination database uses the UTF8MB3 character set, or if the source database uses the GBK, GB18030, or ZHS16GBK character set and the destination database uses the GBK, GB2312, or GB18030 character set, some characters may be incompatible due to inconsistent character set encoding ranges (GB18030_2022 > GB18030 > GBK> GB2312) or database differences, some data may contain garbled characters, data may be inconsistent after synchronization, or data may fail to be written into the destination database. The destination database object must meet the following requirements: The destination database has sufficient disk space. Before the synchronization, ensure that the corresponding database has been created in the destination instance. Before synchronization, ensure that the table structure of the destination database has been created and is the same as that of the source database or contains all columns in the source database. The destination table can contain more columns than the source table. However, the following failures must be avoided: Assume that extra columns on the destination cannot be null or have default values. If newly inserted data records are synchronized from the source to the destination, the extra columns will become null, which does not meet the requirements of the destination and will cause the task to fail. Assume that extra columns on the destination must be fixed at a default value and have a unique constraint. If newly inserted data records are synchronized from the source to the destination, the extra columns will contain multiple default values. That does not meet the unique constraint of the destination and will cause the task to fail. Before full synchronization, ensure that there is no data in the destination database table. Otherwise, data may be inconsistent or the task may fail. If retry upon failure or resumable transfer occurs during full synchronization, the truncate command is executed to clear data in tables without primary keys in the destination database that have not been synchronized, and then the tables are synchronized again. Before full synchronization, ensure that the synchronization user has the TRUNCATE permission on the tables without primary keys in the destination database. Otherwise, the task may fail. Other notes: If the DCC does not support instances with 4 vCPUs and 8 GB memory or higher instance specifications, the synchronization task cannot be created. By default, the GaussDB-to-MySQL synchronization task does not support loopback and cascading synchronization. That is, data cannot be synchronized from instance A to instance B and then from instance B to instance C. The names (case-sensitive) of objects, such as tables and schemas, in the source database must be the same as those in the destination database. If a logical replication slot fails to be created or does not exist due to a long transaction, you can reset the task and then restart it. Before creating a DRS task, if concurrency control rules of SQL statements are configured for the destination database, the DRS task may fail. Restricted by the logical replication capability of GaussDB, up to 20 logical replication slots can be enabled for decoding on the same instance. In GaussDB, if there is 0x00 in character or binary data, the data will be truncated, which is inconsistent with MySQL. As a result, the final data may be inconsistent. Binary data cannot be used as a DML matching condition. That is, binary data cannot be used as a primary key. Binary data is fixed in length and is automatically filled in. The fill character of GaussDB is 0x20, and that of MySQL is 0x00. Source database version earlier than 94563 and GaussDB B- or MySQL-compatible mode: If b_format is enabled (for example, set b_format_version = 's1', set b_format_dev_version = 's1', or set b_format_dev_version = 's2'), TIMESTAMP WITH TIME ZONE data cannot be synchronized. To query the source database version, run the following SQL statement: select working_version_num();
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 run 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.
Incremental 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. Before a task enters the incremental synchronization phase, ensure that long-running transactions are not started in the source database. Starting the long transaction will block the creation of the logical replication slot and cause the task to fail. Do not execute any DDL statement in the source database. Restricted by the GaussDB logical replication function, DDL statements cannot be synchronized. If you synchronize DDL statements, data may be inconsistent or the task may fail. Do not change the REPLICA IDENTITY value of a table in the source database. Otherwise, incremental 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. Replication of interval partition tables is not supported. After a DDL statement is executed in a transaction, the DDL statement and subsequent statements are not synchronized. Logical log decoding is restricted by the decoding capability of the GaussDB kernel. For details about the restrictions, see the precautions in "Logical Decoding" of GaussDB Developer Guide.
Synchronization comparison	You are advised to compare data in the source database during off-peak hours to prevent inconsistent data from being falsely reported and reduce the impact on the source database and DRS tasks. During incremental synchronization, if data is written to the source database, the comparison results may be inconsistent. Do not limit the synchronization speed during data comparison. MySQL and GaussDB process zero time (0000-00-00 00:00:00) in different ways. During value comparison, if there is zero time in the source or destination database, the comparison result shows that data is inconsistent.
Stopping a task	Stop a task normally. After the task is complete, the streaming replication slot created in the source database is automatically deleted. Forcibly stop a task. To forcibly stop a synchronization task, you need to manually delete the replication slots that may remain in the source database. For details, see Forcibly Stopping Synchronization of GaussDB Primary/Standby. The naming rule of a replication slot depends on the database kernel version (you can run the select working_version_num(); command to view the version). If the version is earlier than 92556, serial decoding is used by default. The naming rule of a replication slot is replication_slot_unique_ID. If the version is 92556 or later, parallel decoding is used by default. The naming rule of a replication slot is drs_unique_ID. To obtain the unique ID, replace the hyphen (-) in the task node ID with an underscore (_). You can find the node ID in the task node id is *** log on the Synchronization Logs page.

Prerequisites

You have logged in to the DRS console.
Your account balance is greater than or equal to $0 USD.
For details about the DB types and versions supported by real-time synchronization, see Supported Databases.
If a subaccount is used to create a DRS task, ensure that an agency has been added. To create an agency, see Agency Management.

You have read Precautions.

Procedure

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 details

Figure 2 Synchronization instance details

**Table 6** Synchronization instance settings
Parameter	Description
Data Flow	Choose Self-built to self-built.
Source DB Engine	Select GaussDB Primary/Standby.
Destination DB Engine	Select MySQL.
Network Type	Public network is used as an example. Available options: Public network and VPN or Direct Connect
VPC	Select an available VPC.
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. If you select VPN or Direct Connect for Network Type, you can enter a specified IP address. When creating multiple tasks at the same time, do not specify the same group of unused IP addresses. Otherwise, the tasks fail to be created.
Security Group	Select a security group. You can use security group rules to allow or deny access to the instance.
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.
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.

Task Type

Figure 3 Task type

**Table 7** Task type information
Parameter	Description
Specifications	DRS instance specifications. Different specifications have different performance upper limits. For details, see Real-Time Synchronization. NOTE: DRS allows you to upgrade specifications only for single-AZ synchronization tasks. Task specifications cannot be downgraded. For details, see Changing Specifications.
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, 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. 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. For details, see Network Preparations.
Account connectivity: Ensure that the source and destination databases allows connections from the DRS instance using the username and password.

Figure 5 Source database information

**Table 9** Source database settings
Parameter	Description
DR Synchronization	If enabled, the source database is a cluster deployed in the DR mode. Information about all nodes in the DR cluster must be entered in IP Address or Domain Name.
IP Address or Domain Name	Enter the IP addresses of GaussDB. Ensure that the entered IP addresses or domain names belong to the same instance and enter the IP addresses of all primary and standby instances.
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 the database and the synchronization instance during the synchronization. After the task is deleted, the username and password are permanently deleted.

Figure 6 Destination database information

**Table 10** 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
Port	The port of the destination database. Range: 1 - 65535
Database Username	The username for accessing the destination 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.

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.

Figure 7 Synchronization mode

**Table 11** Synchronization 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.
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. If the synchronized data conflicts with the existing data in the destination database, selecting Ignore cannot ensure data consistency. To ensure data consistency, select Overwrite.
Synchronize DML	Select the DML operations to be synchronized. By default, all DML operations are selected. If you do not select Delete, DELETE statements in the incremental data of the source database will not be synchronized, which may cause a data inconsistency. As a result, there may be a data conflict or the task may fail.
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 files for Synchronization Object 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 is c_, 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: 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 Process Data page, set the filtering rules for data processing.
- If data processing is not required, click Next.
- If you need to filter out data, set the corresponding rules by referring to Processing Data.
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.

From GaussDB Primary/Standby to MySQL