Two-way data synchronization between PostgreSQL instances-Data Transmission Service(DTS)-阿里云帮助中心

DTS supports real-time, two-way data synchronization between two PostgreSQL databases, such as ApsaraDB RDS for PostgreSQL and self-managed PostgreSQL. This feature supports use cases such as active geo-redundancy (cell-based architecture) and geo-disaster recovery. This topic uses two-way synchronization between ApsaraDB RDS for PostgreSQL instances as an example to walk you through the configuration steps. The configuration process for other data sources is similar.

Prerequisites

The source and destination ApsaraDB RDS for PostgreSQL instances must be created. For instructions, see Create an ApsaraDB RDS for PostgreSQL instance.

Note
For the supported versions of the source and destination databases, see synchronization solution overview.
Set the wal_level parameter to logical for the source and destination ApsaraDB RDS for PostgreSQL instances. For instructions, see Set instance parameters.

Limitations

Type	Description
Source and destination database limits	If the tables to be synchronized do not have primary keys or UNIQUE constraints, you must enable the Exactly-Once write feature when you configure the task. Otherwise, duplicate data may exist in the destination database. For more information, see Synchronize tables without primary keys or UNIQUE constraints. The name of the database to be synchronized cannot contain hyphens (-), such as dts-testdata. If you synchronize data at the table level and need to edit objects, such as mapping column names, and the number of tables in a single synchronization task exceeds 5,000, split the tables into multiple tasks or configure a task to synchronize the entire database. Otherwise, a request error may be reported after you submit the task. DTS does not synchronize temporary tables, internal triggers, or some functions (C language functions and internal functions for PROCEDURE and FUNCTION) from the source database. DTS synchronizes some custom data types (COMPOSITE, ENUM, or RANGE) and the following constraints: primary key, foreign key, unique, and CHECK. Write-ahead log (WAL): WAL must be enabled. Set the wal_level parameter to logical. For an incremental synchronization task, DTS requires that the WAL logs in the source database are retained for more than 24 hours. For a task that performs both full and incremental synchronization, DTS requires that the WAL logs are retained for at least 7 days. You can change the log retention period to more than 24 hours after the initial full data synchronization is complete. If the task fails because DTS cannot obtain the required WAL logs, or in extreme cases, data inconsistency or data loss occurs, the issue is not covered by the DTS Service-Level Agreement (SLA) because the specified log retention period is shorter than required. Source database operation limits To ensure that the sync task runs properly and to prevent logical replication interruptions during a failover, you must enable Logical Replication Slot Failover for ApsaraDB RDS for PostgreSQL. For more information, see Logical Replication Slot Failover. Due to the limits of logical replication in the source database, if a single piece of data to be synchronized exceeds 256 MB after an incremental change, the synchronization instance may fail and cannot be recovered. You must reconfigure the synchronization instance. Do not run DDL operations that change database or table schemas during schema synchronization or full synchronization. Otherwise, the synchronization task fails. Note During full synchronization, DTS queries the source database. This creates metadata locks that may block DDL operations on the source database. If the source database has long-running transactions and the instance includes an incremental synchronization task, the write-ahead logs (WALs) generated before the long-running transactions are committed cannot be cleared and may accumulate. This can cause the disk space of the source database to become insufficient. If you perform a major engine version upgrade on the source database while the synchronization instance is running, the instance fails and cannot be recovered. You must reconfigure the synchronization instance.
Other limits	A single data synchronization task can synchronize only one database. To synchronize multiple databases, you must configure a data synchronization task for each database. DTS does not synchronize TimescaleDB extension tables, tables with cross-schema inheritance, or tables that contain expression-based unique indexes. If a two-way synchronization instance in the China (Chengdu) or China (Shanghai) region includes a full data synchronization task, DTS creates a full data verification task for that instance by default. For this verification task, Full Data Verification is set to Verify based on the number of table rows. If you have already configured a full data verification task, your configuration takes precedence. If a table to be synchronized contains a SERIAL field, the source database automatically creates a Sequence for the field. Therefore, when you configure Source Objects, if you select Schema Synchronization for Synchronization Types, we recommend that you also select Sequence or synchronize the entire schema. Otherwise, the synchronization instance may fail. In the following three scenarios, you must run the `ALTER TABLE schema.table REPLICA IDENTITY FULL;` command on the tables to be synchronized before you write data to them. This ensures data consistency. Do not perform table locking operations during the execution of this command. Otherwise, the tables may be locked. If you skip the related check items in the precheck, DTS automatically runs this command during the initialization of the instance. When the instance runs for the first time. When the synchronization granularity is schema, and a new table is created in the schema to be synchronized or a table to be synchronized is rebuilt using the RENAME command. When you use the Modify Objects feature. Note In the command, replace `schema` and `table` with the names of the schema and table to which the data to be synchronized belongs. Perform this operation during off-peak hours. DTS validates data content but does not validate metadata such as sequences. You must validate the metadata yourself. After you switch your business to the destination instance, new sequences do not increment from the maximum value of the sequences in the source database. Before the switchover, you must query the maximum value of the corresponding sequence in the source database and then set it as the initial value of the corresponding sequence in the destination database. The following command queries the sequence values in the source database: `do language plpgsql $$ declare nsp name; rel name; val int8; begin for nsp,rel in select nspname,relname from pg_class t2 , pg_namespace t3 where t2.relnamespace=t3.oid and t2.relkind='S' loop execute format($_$select last_value from %I.%I$_$, nsp, rel) into val; raise notice '%', format($_$select setval('%I.%I'::regclass, %s);$_$, nsp, rel, val+1); end loop; end; $$;` Note The SQL statements that are returned after you run the preceding command contain all sequences of the source database. Run the SQL statements in the destination database as needed. DTS creates the following temporary tables in the source database to obtain the DDL statements of incremental data, the structure of incremental tables, and heartbeat information. During synchronization, do not delete these temporary tables. Otherwise, the DTS task becomes abnormal. The temporary tables are automatically deleted after the DTS instance is released. `public.dts_pg_class`, `public.dts_pg_attribute`, `public.dts_pg_type`, `public.dts_pg_enum`, `public.dts_postgres_heartbeat`, `public.dts_ddl_command`, `public.dts_args_session`, and `public.aliyun_dts_instance`. To ensure the accuracy of the displayed synchronization latency, DTS adds a heartbeat table named dts_postgres_heartbeat to the source database. During data synchronization, DTS creates a replication slot with the prefix `dts_sync_` in the source database to replicate data. DTS uses this replication slot to obtain incremental logs from the source database within 15 minutes. When the data synchronization fails or the synchronization instance is released, DTS attempts to automatically clear this replication slot. Note If you change the password of the database account used by the task or delete the DTS IP address whitelist from the source database during data synchronization, the replication slot cannot be automatically cleared. In this case, you must manually clear the replication slot in the source database to prevent it from accumulating and occupying disk space, which can make the source database unavailable. If a failover occurs on the source database, you must log on to the secondary database to manually clear the replication slot. Evaluate the performance of the source and destination databases before you synchronize data. Synchronize data during off-peak hours. Otherwise, initial full data synchronization consumes read and write resources on the source and destination databases, which may increase the database load. Initial full data synchronization runs concurrent INSERT operations, which causes table fragmentation in the destination database. As a result, the tablespace of the destination instance is larger than that of the source instance after the initial full data synchronization is complete. For table-level data synchronization, if no data other than the data from DTS is written to the destination database, you can use Data Management (DMS) to perform online DDL operations. For more information, see Perform schema changes without table locks. During DTS synchronization, do not write data other than the data from DTS to the destination database. Otherwise, data inconsistency occurs between the source and destination databases. For example, if you use DMS to perform online DDL operations while other data is being written to the destination database, data may be lost in the destination database. For a task that performs full or incremental synchronization, if the tables to be synchronized in the source database contain foreign keys, triggers, or event triggers, and the destination database account is a privileged account or has superuser permissions, DTS temporarily sets the session_replication_role parameter to replica at the session level during synchronization. If the destination database account does not have these permissions, you must manually set the session_replication_role parameter to replica in the destination database. During this period (when session_replication_role is set to replica), if cascade update or delete operations occur in the source database, data inconsistency may occur. After the DTS task is released, you can change the value of the session_replication_role parameter back to origin. A two-way synchronization task includes forward and reverse synchronization tasks. When you configure or reset the task, if the destination object of one task matches the synchronization object of the other task: Allow only one task to synchronize full and incremental data. The other task supports only incremental synchronization. Data from the source of the current task synchronizes only to the destination of the current task. It does not serve as source data for the other task. If a task fails, DTS support staff will attempt to restore it within eight hours. During restoration, they may restart the task or adjust its parameters. Note Only DTS task parameters are modified—not database parameters. Parameters that may be adjusted include those listed in Modify instance parameters. When you synchronize partitioned tables, you must include both the parent table and its child tables as synchronization objects. Otherwise, data inconsistency may occur in the partitioned table. Note The parent table of a PostgreSQL partitioned table does not directly store data. All data is stored in the child tables. The synchronization task must include the parent table and all its child tables. Otherwise, data in the child tables may not be synchronized, leading to data inconsistency between the source and destination.
Special cases	When the source instance is an ApsaraDB RDS for PostgreSQL instance During synchronization, do not change the endpoint or zone of the ApsaraDB RDS for PostgreSQL instance. Otherwise, the synchronization fails. When the source instance is a self-managed PostgreSQL database Make sure that the values of the max_wal_senders and max_replication_slots parameters are greater than the sum of the number of replication slots in use and the number of DTS instances to be created with this self-managed PostgreSQL database as the source. When the source instance is Google Cloud Platform Cloud SQL for PostgreSQL, the Database Account for the source database must have the `cloudsqlsuperuser` permission. When you select synchronization objects, you must select objects that this account is authorized to manage, or grant the Owner permission for the objects to be synchronized to this account (for example, by running the `GRANT <owner_of_the_object_to_be_synchronized> TO <source_database_account_used_by_the_task>` command to allow this account to perform related operations as the object owner). Note An account with the cloudsqlsuperuser permission cannot manage data whose owner is another account with the cloudsqlsuperuser permission.

Billing

Synchronization type	Pricing
Schema synchronization and full data synchronization	Free of charge.
Incremental data synchronization	Charged. For more information, see Billing overview.

Two-way synchronization topologies

DTS supports two-way data synchronization between only two PostgreSQL databases.

Supported conflict detection

To ensure data consistency, make sure that data records with the same primary key, business primary key, or unique key are updated in only one of the database instances in the two-way synchronization. If data records are updated on both database instances, DTS the system will apply the conflict resolution policy configured in the task.

DTS checks and fixes conflicts to maximize the stability of two-way synchronization tasks. DTS can detect the following types of conflicts:

Uniqueness conflicts caused by INSERT operations

In two-way synchronization, if records with the same primary key are inserted into both database instances simultaneously (or in close succession), a uniqueness constraint conflict will be triggered. When the INSERT statement is synchronized to the peer instance, it will fail because a record with the same primary key value already exists.
Mismatched records in UPDATE operations
- If the records to be updated do not exist in the destination instance, DTS converts the UPDATE operation into an INSERT operation. However, uniqueness conflicts may occur.
- The record to be updated by an UPDATE operation causes a primary key or unique key conflict.
Non-existent records to be deleted

The records to be deleted do not exist in the destination instance. In this case, DTS ignores the DELETE operation regardless of the conflict resolution policy that you specify.

Important

Due to time differences and latency, DTS cannot guarantee 100% conflict prevention. To ensure consistency, update records with the same primary or unique key on only one database instance at a time.
DTS provides various conflict resolution strategies for the aforementioned data conflicts, which you can select while configuring two-way data synchronization.

Supported objects

Object type	Details
SCHEMA and TABLE	Includes PRIMARY KEY, UNIQUE KEY, FOREIGN KEY, built-in data types, and DEFAULT CONSTRAINT
Other objects	VIEW, PROCEDURE (PostgreSQL V11 or later), FUNCTION, RULE, SEQUENCE, EXTENSION, TRIGGER, AGGREGATE, INDEX, OPERATOR, DOMAIN

Supported SQL operations

Operation type	SQL operations
DML	`INSERT`, `UPDATE`, and `DELETE`
DDL	Only data synchronization tasks created after October 1, 2020 (Beijing time)October 1, 2020 (Singapore time) support DDL operations. Important For data synchronization tasks created before September 9, 2022 (Beijing time), you must create a trigger and a function in the source database to capture DDL information before you configure the task. For more information, see Implement incremental DDL migration for PostgreSQL by using triggers and functions. Data of the bit type cannot be synchronized during incremental data synchronization. A data synchronization task supports the following DDL statements. This requires a high-privilege account for the source database, and the minor kernel version of an ApsaraDB RDS for PostgreSQL instance must be 20210228 or later. For more information about how to upgrade the minor kernel version, see Upgrade a minor kernel version. `CREATE TABLE`, `DROP TABLE` `ALTER TABLE` (including `RENAME TABLE`, `ADD COLUMN`, `ADD COLUMN DEFAULT`, `ALTER COLUMN TYPE`, `DROP COLUMN`, `ADD CONSTRAINT`, `ADD CONSTRAINT CHECK`, and `ALTER COLUMN DROP DEFAULT`) `TRUNCATE TABLE` (if the source database is PostgreSQL 11 or later) `CREATE INDEX ON TABLE` Important The synchronization process excludes additional clauses in DDL statements, such as `CASCADE` or `RESTRICT`. The synchronization process excludes DDL statements from a session that runs the `SET session_replication_role = replica` command. The synchronization process excludes DDL statements executed by calling a `FUNCTION` or by using similar methods. If a single transaction in the source database contains both DML and DDL statements, the synchronization process excludes the DDL statements. If a single transaction in the source database includes DDL statements for non-synchronized objects, the synchronization process excludes those DDL statements. The synchronization process excludes DDL statements executed directly in a plugin by using the SPI.

Important

Only the forward task (from the source database to the destination database) supports DDL synchronization. The reverse task (from the destination database to the source database) does not support DDL synchronization and automatically filters out DDL operations.

Procedure

Purchase a two-way data synchronization instance. For more information, see Purchase a data synchronization task.

Important
On the purchase page, select PostgreSQL for both the PostgreSQL and PostgreSQL, and select Two-way Synchronization for Two-way Synchronization.
Go to the Data Synchronization page of the new DTS console.
Note
Alternatively, log on to the DMS console. In the top menu bar, choose Data + AI. Then, in the navigation pane on the left, choose Data Transmission (DTS) > Data Synchronization.
In the upper-left corner of the page, select the region where the destination instance is located.
Find the data synchronization instance that you purchased and click Configure Task for its first synchronization task.

Configure the source and destination databases.

Warning

After you select the source and destination instances, review the Limits at the top of the page. Otherwise, the task may fail or data inconsistency may occur.

Category	Parameter	Description
N/A	Task Name	DTS automatically generates a task name. We recommend that you specify a descriptive name for easy identification. The name does not need to be unique.
Source Database	Database Type	Select PostgreSQL.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	The region of the source instance that you selected during purchase. This parameter cannot be changed.
	Instance ID	Select the ID of the source ApsaraDB RDS for PostgreSQL instance.
	Database Name	Enter the name of the database that contains the objects to be synchronized in the source ApsaraDB RDS for PostgreSQL instance.
	Database Account	Enter a high-privilege account for the source ApsaraDB RDS for PostgreSQL instance. The account must be the owner of the selected database. For more information about how to create an account and grant permissions, see Create an account and Create a database.
	Database Password	Enter the password for the specified database account.
	Encryption	Select a connection method based on your requirements. In this example, Non-encrypted is selected. To connect to the database using SSL encryption, select SSL-encrypted. Then, upload the required CA Certificate, Client Certificate, and Private Key of Client Certificate, and enter the Private Key Password of Client Certificate. Note If you select SSL-encrypted for a self-managed PostgreSQL database, you must upload the CA Certificate. If you need to use a client certificate, you must upload both the Client Certificate and the Private Key of Client Certificate, and enter the Private Key Password of Client Certificate. For information about the SSL encryption feature for ApsaraDB RDS for PostgreSQL instances, see SSL encryption.
Destination Database	Database Type	Select PostgreSQL.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	The region of the destination instance that you selected during purchase. This parameter cannot be changed.
	Instance ID	Select the ID of the destination ApsaraDB RDS for PostgreSQL instance.
	Database Name	Enter the name of the database that contains the objects to be synchronized in the destination ApsaraDB RDS for PostgreSQL instance.
	Database Account	Enter a high-privilege account for the destination ApsaraDB RDS for PostgreSQL instance. The account must be the owner of the selected database. For more information about how to create an account and grant permissions, see Create an account and Create a database.
	Database Password	Enter the password for the specified database account.
	Encryption	Select a connection method based on your requirements. In this example, Non-encrypted is selected. To connect to the database using SSL encryption, select SSL-encrypted. Then, upload the required CA Certificate, Client Certificate, and Private Key of Client Certificate, and enter the Private Key Password of Client Certificate. Note If you select SSL-encrypted for a self-managed PostgreSQL database, you must upload the CA Certificate. If you need to use a client certificate, you must upload both the Client Certificate and the Private Key of Client Certificate, and enter the Private Key Password of Client Certificate. For information about the SSL encryption feature for ApsaraDB RDS for PostgreSQL instances, see SSL encryption.

After completing the configuration, click Test Connectivity and Proceed at the bottom of the page.
Note
- Ensure that you add the CIDR blocks of the DTS servers (either automatically or manually) to the security settings of both the source and destination databases to allow access. For more information, see Add the IP address whitelist of DTS servers.
- If the source or destination is a self-managed database (i.e., the Access Method is not Alibaba Cloud Instance), you must also click Test Connectivity in the CIDR Blocks of DTS Servers dialog box.

Configure the task objects.

On the Configure Objects page, specify the objects to synchronize.

Parameter	Description
Synchronization Types	DTS always selects Incremental Data Synchronization. By default, you must also select Schema Synchronization and Full Data Synchronization. After the precheck, DTS initializes the destination cluster with the full data of the selected source objects, which serves as the baseline for subsequent incremental synchronization. Note If you select Schema Synchronization, DTS synchronizes the schemas of the tables to be synchronized, including foreign keys, from the source database to the destination database.
Processing Mode of Conflicting Tables	Precheck and Report Errors: Checks for tables with the same names in the destination database. If any tables with the same names are found, an error is reported during the precheck and the data synchronization task does not start. Otherwise, the precheck is successful. Note If you cannot delete or rename the table with the same name in the destination database, you can map it to a different name in the destination. For more information, see Database Table Column Name Mapping. Ignore Errors and Proceed: Skips the check for tables with the same name in the destination database. Warning Selecting Ignore Errors and Proceed may cause data inconsistency and put your business at risk. For example: If the table schemas are consistent and a record in the destination database has the same primary key or unique key value as a record in the source database: During full data synchronization, DTS retains the destination record and skips the source record. During incremental synchronization, DTS overwrites the destination record with the source record. If the table schemas are inconsistent, data initialization may fail. This can result in only partial data synchronization or a complete synchronization failure. Use with caution.
Synchronization Topology	Select Two-way Synchronization.
Exclude DDL Operations	Yes: DDL operations are not synchronized. No: DDL operations are synchronized. Important To ensure the stability of the two-way synchronization link, you can choose whether to synchronize DDL operations only for the forward synchronization task (from the source database to the destination database). For the reverse synchronization task (from the destination database to the source database), DDL operations are automatically filtered out.
Conflict Resolution Policy	If you encounter the preceding conflict types, select a conflict resolution policy based on your business requirements. TaskFailed (Fail and report an error upon conflict) The task will error out and stop if a conflict occurs. The task enters a failed state and requires manual intervention for recovery. Ignore (Keep the existing record in the destination instance) The system skips the conflicting statement and continues the synchronization. The existing record in the destination instance is retained. Overwrite (Overwrite the conflicting record in the destination instance) If a conflict occurs, the system overwrites the conflicting record in the destination instance with the data from the source. Note If a synchronization task experiences latency after being paused or restarted, these policies do not take effect during the latency period. Data in the destination database is overwritten by default.
Capitalization of Object Names in Destination Instance	Configure the case-sensitivity policy for database, table, and column names in the destination instance. By default, the DTS default policy is selected. You can also choose to use the default policy of the source or destination database. For more information, see Case policy for destination object names.
Source Objects	In the Source Objects box, click the objects, and then click to move them to the Selected Objects box. Note You can select objects to synchronize at the schema or table level. If you select tables as synchronization objects, other objects such as views, triggers, and stored procedures are not synchronized to the destination database. If a table to be synchronized contains a field of the SERIAL type and you select Schema Synchronization for Synchronization Types, we recommend that you also select Sequence or synchronize the entire schema.
Selected Objects	To rename a single object in the destination instance, right-click the object in the Selected Objects box. For more information, see Map a single object name. To rename multiple objects in bulk, click Batch Edit in the upper-right corner of the Selected Objects box. For more information, see Map multiple object names in bulk. Note To select the SQL operations to synchronize for a specific schema or table, right-click the object in the Selected Objects box. In the dialog box that appears, select the desired SQL operations. To specify WHERE conditions to filter data, right-click a table in the Selected Objects box. In the dialog box that appears, specify the filter conditions. For more information, see Use SQL conditions to filter data. If you use the object name mapping feature to rename an object, other objects that depend on the renamed object may fail to be synchronized.

Click Next: Advanced Settings.

Parameter	Description
Dedicated Cluster for Task Scheduling	By default, DTS uses a shared cluster for tasks, so you do not need to make a selection. For greater task stability, you can purchase a dedicated cluster to run the DTS synchronization task. For more information, see What is a DTS dedicated cluster?.
Retry Time for Failed Connections	If the connection to the source or destination database fails after the synchronization task starts, DTS reports an error and immediately begins to retry the connection. The default retry duration is 720 minutes. You can customize the retry time to a value from 10 to 1,440 minutes. We recommend a duration of 30 minutes or more. If the connection is restored within this period, the task resumes automatically. Otherwise, the task fails. Note If multiple DTS instances (e.g., Instance A and B) share a source or destination, DTS uses the shortest configured retry duration (e.g., 30 minutes for A, 60 for B, so 30 minutes is used) for all instances. DTS charges for task runtime during connection retries. Set a custom duration based on your business needs, or release the DTS instance promptly after you release the source/destination instances.
Retry Time for Other Issues	If a non-connection issue (e.g., a DDL or DML execution error) occurs, DTS reports an error and immediately retries the operation. The default retry duration is 10 minutes. You can also customize the retry time to a value from 1 to 1,440 minutes. We recommend a duration of 10 minutes or more. If the related operations succeed within the set retry time, the synchronization task automatically resumes. Otherwise, the task fails. Important The value of Retry Time for Other Issues must be less than that of Retry Time for Failed Connections.
Enable Throttling for Full Data Synchronization	During full data synchronization, DTS consumes read and write resources from the source and destination databases, which can increase their load. To mitigate pressure on the destination database, you can limit the migration rate by setting Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s). Note This parameter is available only if Synchronization Types is set to Full Data Synchronization. You can also adjust the rate of full data synchronization when the synchronization instance is running.
Enable Throttling for Incremental Data Synchronization	You can also limit the incremental synchronization rate to reduce pressure on the destination database by setting RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s).
Environment Tag	You can select an environment tag to identify the instance based on your business requirements. In this example, you do not need to select a tag.
Configure ETL	Choose whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: Enables the ETL feature. Enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: Disables the ETL feature.
Monitoring and Alerting	Choose whether to set up alerts. If the synchronization fails or the latency exceeds the specified threshold, DTS sends a notification to the alert contacts. No: No alerts are configured. Yes: Configures alerts. You must also set the alert threshold and alert contact. For more information, see Configure monitoring and alerting during task configuration.

Click Data Verification to configure a data verification task.
To use the data verification feature, see Configure data verification.

Save the task and perform a precheck.
- To view the parameters for configuring this instance via an API operation, hover over the Next: Save Task Settings and Precheck button and click Preview OpenAPI parameters in the tooltip.
- If you have finished viewing the API parameters, click Next: Save Task Settings and Precheck at the bottom of the page.
Note
- Before a synchronization task starts, DTS performs a precheck. You can start the task only if the precheck passes.
- If the precheck fails, click View Details next to the failed item, fix the issue as prompted, and then rerun the precheck.
- If the precheck generates warnings:
  For non-ignorable warning, click View Details next to the item, fix the issue as prompted, and run the precheck again.
  For ignorable warnings, you can bypass them by clicking Confirm Alert Details, then Ignore, and then OK. Finally, click Precheck Again to skip the warning and run the precheck again. Ignoring precheck warnings may lead to data inconsistencies and other business risks. Proceed with caution.
When the Success Rate is 100%, click Back.
Configure the reverse synchronization task.
1. Wait until the Status of the forward synchronization task changes to Running.
2. Locate the reverse synchronization task and click Configure Task.
3. Configure the reverse synchronization task by following Step 5 to Step 9.
  Important
  
  When configuring the reverse synchronization task, ensure the source and destination instances are swapped: the destination of the forward task becomes the source of the reverse task, and vice versa. Also, ensure that all other instance information, such as the database name, account, and password, is correct and consistent.
  
  The Instance Region for the source and destination databases of the reverse synchronization task cannot be changed. Fewer parameters are required than for the forward synchronization task. Configure the parameters that are displayed in the console.
  
  The Processing Mode of Conflicting Tables setting for the reverse synchronization task does not check for tables that were synchronized to the destination instance by the forward synchronization task.
  
  The reverse synchronization task does not support synchronizing the objects specified in the Selected Objects list of the forward synchronization task.
  
  We recommend that you do not use the object name mapping feature when you configure the reverse synchronization task. Otherwise, data inconsistency may occur.
After the reverse synchronization task is configured, wait for the Status of both tasks to change to Running. The two-way data synchronization is fully configured.