From PostgreSQL to PostgreSQL_Data Replication Service

Supported Source and Destination Databases

**Table 1** Supported databases
Source DB	Destination DB
RDS for PostgreSQL (versions 9.5, 9.6, 10, 11, 12, 13, 14 and 15)	On-premises databases (PostgreSQL 9.5, 9.6, 10, 11, 12, 13, 14 and 15) ECS-hosted databases (PostgreSQL 9.5, 9.6, 10, 11, 12, 13, 14 and 15) NOTE: The major version of the destination database must be the same as or later than that of the source database.

Supported Synchronization Objects

Table 2 lists the objects that can be synchronized in different scenarios. DRS will automatically check the objects you selected before the synchronization.

**Table 2** Supported synchronization objects
Type	Notes
Objects	Instance-level synchronization is not supported. Only one database can be synchronized at a time. Multiple DRS tasks are required to synchronize multiple databases. Supported field types: Digit, currency, character, binary, date/time, boolean, enumeration, geometry, network address, bit, text search, UUID, XML, JSON, array, compound, and range. Scope of full synchronization The following objects are supported in the database-level synchronization: schemas, tables, indexes, constraints, views, materialized views, sequences, stored procedures, rules, triggers, foreign keys, sorting rules, plug-ins, code conversion information, aggregate functions, operators, statistics extension, conversion information, text search configurations, functions, data types, type conversion, event triggers, text search parsers, and text search templates During the table-level synchronization, only tables, views, materialized views, sequences, and common indexes can be synchronized. During object file import, tables can be synchronized. System objects such as system schemas, system tables, system users, and system functions cannot be synchronized. Other objects such as tablespaces, foreign data wrappers, foreign servers, user mappings, releases, subscriptions, and users cannot be synchronized. Object permissions cannot be synchronized. NOTE: The restrictions on the objects that can be synchronized are as follows: Object name: The database name cannot contain +"%'\<>, the schema name and table name cannot contain ".'<>, and the column name cannot contain double quotation marks (") and single quotation marks ('). Table: Temporary tables are not synchronized. During table-level synchronization, table constraints, indexes, and rules are synchronized, except for table triggers. Function: Do not synchronize C language functions or functions with the leakproof or support attribute. Plug-in: The metadata of plug-ins is not synchronized. Data type: Basic data types are not synchronized. Type conversion: The binary coercion type cannot be converted. Scope of incremental synchronization Some DML statements, including INSERT, UPDATE, and DELETE, can be synchronized. Some DDL statements can be synchronized, including TRUNCATE (only for PostgreSQL 11 or later), CREATE SCHEMA, CREATE TABLE, DROP TABLE, ALTER TABLE (including ADD COLUMN, DROP COLUMN, ALTER COLUMN, RENAME COLUMN, ADD CONSTRAINT, DROP CONSTRAINT and RENAME), CREATE SEQUENCE, DROP SEQUENCE, ALTER SEQUENCE, CREATE INDEX, ALTER INDEX, DROP INDEX, CREATE VIEW, ALTER VIEW, COMMENT ON COLUMN, COMMENT ON TABLE, COMMENT ON SCHEMA, COMMENT ON SEQUENCE, COMMENT ON INDEX, and COMMENT ON VIEW. During table-level synchronization, only the following DDL operations can be synchronized: TRUNCATE (only for PostgreSQL 11 or later), DROP TABLE, COMMENT ON COLUMN, COMMENT ON TABLE, and ALTER TABLE (including ADD COLUMN, DROP COLUMN, ALTER COLUMN, RENAME COLUMN, ADD CONSTRAINT, DROP CONSTRAINT and RENAME). Not synchronized: DML statements of unlogged tables and temporary tables NOTE: The source database captures DDL statements using event triggers and records them in specific tables, so you need to create event triggers and functions in the source database in advance. For details, see Creating Event Triggers and Functions to Implement Incremental DDL Synchronization for PostgreSQL. Incremental heartbeat information sending: For PostgreSQL 9.6 and later versions, if no data is written to the source database for a long time (more than 10 hours), the log extraction process invokes pg_logical_emit_message to insert heartbeat information into WAL logs of the source database, which ensures that the logical replication slot number is updated normally. (Only WAL logs are added, and services are not affected.)

Database Account Permission Requirements

To start a synchronization task, the source and destination database users must meet the requirements in the following table. Different types of synchronization tasks require different permissions. For details, see Table 3. DRS automatically checks the database account permissions in the pre-check phase and provides handling suggestions.

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 account permission
Type	Full	Full+Incremental
Source database user	Database CONNECT permission, schema USAGE permission, table SELECT permission, and sequence SELECT permission	The CONNECT permission for databases, the USAGE permission for schemas, the SELECT permission for tables, the SELECT permissions for sequences, the UPDATE, DELETE, and TRUNCATE permissions for tables that do not have primary keys, and the permission to create replication connections NOTE: The UPDATE, DELETE, and TRUNCATE permissions for tables that do not have primary keys are only used to temporarily lock tables to ensure data consistency after the migration.
Destination database user	Database-level: If the destination database is not PostgreSQL, the CREATEDB permission is required. If the destination database is PostgreSQL, the CONNECT and CREATE permissions on PostgreSQL databases and the USAGE and CREATE permissions on public schemas are required. Table-level: To synchronize databases, the CREATEDB permission is required. To synchronize a schema, the CONNECT and CREATE permissions for the database that contains the schema are required. To synchronize objects in a schema, the CONNECT permission for the database that contains the schema, and the USAGE and CREATE permissions for the schema that contain the object are required. NOTE: If the destination database version is PostgreSQL 15 and no database is created on the destination database for database-level synchronization and table-level synchronization, full or incremental synchronization may fail due to lack of the USAGE and CREATE permissions of the public schema.

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.
- 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.
- For more information about the impact of DRS on databases, see How Does DRS Affect the Source and Destination Databases?
Data-Level Comparison
To obtain accurate comparison results, start data comparison at a specified time point during off-peak hours. If it is needed, select Start at a specified time for Comparison Time. Due to slight time difference and continuous operations on data, data inconsistency may occur, reducing the reliability and validity of the comparison results.

Precautions

The full+incremental synchronization process consists of four phases: task startup, full synchronization, incremental synchronization, and task completion. (A single incremental synchronization task or a single full synchronization task contains three phases.) To ensure smooth synchronization, read the following notes before creating a synchronization task.

**Table 4** Precautions
Type	Constraints
Starting a task	Source database parameter requirements: The partition table trigger of the source database cannot be set to disable. For a full synchronization task, the source database can be a standby database, but hot_standby_feedback must be set to on. For an incremental synchronization task, the source database cannot be a standby database. To perform incremental synchronization: The wal_level value of the source database must be logical. The replica identity attribute of tables that do not have primary keys in the source database must be full. The max_replication_slots value of the source database must be greater than the number of used replication slots. The max_wal_senders value of the source database must be greater than or equal to the max_replication_slots value. If the toast attribute of the primary key column in the source database is main, external, or extended, the replica identity attribute must be full. Source database object requirements: Triggers with the same name cannot exist in the source database. The objects that have dependencies must be synchronized at the same time. Otherwise, the synchronization may fail. Destination database parameter requirements: The block_size value of the destination database must be greater than or equal to that of the source database. The lc_monetary values of the source and destination databases must be the same. To perform incremental synchronization, if the synchronization object contains foreign keys, triggers, or event triggers, set session_replication_role of the destination database to replica. After the synchronization is complete, change the value to the original one. Destination database object requirements: The destination database cannot contain objects with the same type and name as the objects to be synchronized, including databases, schemas, and tables. System databases, system schemas, and system tables are excluded. 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: When a schema name or table name is mapped, to prevent conflicts between indexes and constraint names, the original index name in the table is changed to the following format after synchronization: i_+hash value+original index name (which may be truncated)+_key The hash value is calculated based on the original schema name_original table name_original index name. Similarly, the original constraint name on the table is changed to c_ + hash value + original constraint name (which may be truncated) + _key. Before starting a full+incremental or incremental synchronization task, ensure that no long transaction is started in the source database. Starting the long transaction will block the creation of the logical replication slot and cause the task to fail. For a full+incremental or incremental synchronization task, if an internal error occurs during the pre-check and the task stops before it is started, check and delete the streaming replication slot by referring to Forcibly Stopping Synchronization of PostgreSQL to avoid residual streaming replication slots in the source database. After a full+incremental or incremental task is started, a primary/standby switchover can be performed only on the source database of the following versions: RDS for PostgreSQL 12.6 or later and RDS for PostgreSQL 13 or later. If you choose to synchronize DDL statements, ensure that the DDL statements executed on the source database are compatible with the destination database. NOTE: DDL statements are captured using event triggers in the source database, recorded in a specific table, and then synchronized to the destination database. You need to create event triggers and functions in the source database before starting a task. For details, see Creating Event Triggers and Functions to Implement Incremental DDL Synchronization for PostgreSQL.
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. Do not change the primary key or unique key (if the primary key does not exist) of the source database table. Otherwise, incremental data may be inconsistent or the task may fail. Do not modify the replica identity attribute of tables 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. During database-level synchronization, if a table without a primary key is added to the source database, you must set replica identity of the table to full before writing data. Otherwise, data may be inconsistent or the task may fail. During database-level synchronization, if a primary key table is added to the source database and the toast attribute of the primary key column is main, external, or extended, the replica identity attribute of the table must be set to full before writing data. Otherwise, data may be inconsistent or the task may fail.
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. Data cannot be compared during full synchronization. Do not limit the synchronization speed during data comparison.
Stopping a task	Stop a task normally. The destination database sequence value is automatically reset. The auto-increment sequence value is the source database sequence value plus the security margin, and the auto-decrement sequence value is the source database sequence value minus the security margin. The default security margin is 10,000. If users are synchronized, the user memberships are automatically synchronized after the task is complete. When a full synchronization task is complete, the sequence values are compared based on logical consistency. That is, if an auto-increment sequence value is used only when the sequence value of the destination database is greater than or equal to that of the source database, or an auto-decrement sequence value is used only when the sequence value of the destination database is less than or equal to that of the source database, the sequence values in the source database are consistent with those in the destination database. When a full+incremental synchronization task is complete, the streaming replication slot created by the task in the source database is automatically deleted. If the value of session_replication_role of the destination database is replica when the full+incremental synchronization task is complete, change the value to the original one. Forcibly stop a task. You need to manually update the sequence value in the destination database. For details, see Forcibly Stopping Synchronization of PostgreSQL. To forcibly stop a full+incremental real-time synchronization task, you need to manually delete the replication slots that may remain in the source database. For details, see Forcibly Stopping Synchronization of PostgreSQL. If the value of session_replication_role of the destination database is replica, change it to the original value to forcibly stop the full+incremental synchronization task. The naming rule of a logic 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.
Troubleshooting	If any problem occurs during task creation, startup, full synchronization, incremental synchronization, or completion, rectify the fault by referring to Troubleshooting.

Procedure

This section uses out-of-cloud synchronization from PostgreSQL to PostgreSQL as an example to describe how to configure a real-time synchronization task in the VPC network scenario.

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

On the Create Synchronization Instance page, 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	Select Out of the cloud.
Source DB Engine	Select PostgreSQL.
Destination DB Engine	Select PostgreSQL.
Network Type	Available options: VPC, Public network, and VPN or Direct Connect. VPC is used as an example. 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.
Source DB Instance	The RDS for PostgreSQL DB 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	Full+Incremental This synchronization mode allows you to synchronize data in real time. After a full synchronization initializes the destination database, an incremental synchronization parses logs to ensure data consistency between the source and destination databases. Full All objects and data in non-system databases are synchronized to the destination database at a time. This mode is applicable to scenarios where service interruption is acceptable. 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, select the check box before the agreement and click Next.

Establish the connectivity between the DRS instance and the source and destination databases.

Source database configuration

Figure 5 Source database information

**Table 9** Source database settings
Parameter	Description
DB Instance Name	The RDS for PostgreSQL instance you selected when creating the task. The parameter cannot be changed.
Database Username	The username for accessing the source database.
Database Password	The password for the database username.

Destination database configuration

Figure 6 Destination database information

**Table 10** Destination database settings
Parameter	Description
VPC	A dedicated virtual network in which the destination database is located. It isolates networks for different services. You can select an existing VPC or create a VPC.
Subnet	A subnet provides dedicated network resources that are isolated from other networks, improving network security. The subnet must be in the AZ where the destination database resides. You need to enable DHCP for creating the destination database subnet.
IP Address or Domain Name	The IP address or domain name of the destination database.
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.

The username and password of the source and destination databases are encrypted and stored in the databases and the synchronization instance during the synchronization. After the task is deleted, the username and password are permanently deleted.

On the Set Synchronization Task page, select the synchronization policy and synchronization object, 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. Select any of the following conflict policies: Ignore The system will skip the conflicting data and continue the subsequent synchronization process. If you select Ignore, data in the source database may be inconsistent with that in the destination database. Report error The synchronization task will be stopped and fail. Overwrite Conflicting data will be overwritten. 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	Available options: Normal index, Incremental DDLs, and Populate materialized views during the full synchronization phase Populate materialized views during the full synchronization phase: This option takes effect only for materialized views that was populated in the source database. This operation affects the full synchronization performance. You perform this operation after the full synchronization is complete.
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.
Take Snapshot	If you perform a full+incremental migration, you can take a snapshot for your databases. Exporting data in snapshot mode in the full export phase can effectively improve the data synchronization efficiency in the full+incremental export scenario. However, the snapshot mechanism of PostgreSQL prevents historical data in the database from being reclaimed during the export, which may cause space expansion. You are advised to use this method when the full or incremental data volume is large and the source database disk space is sufficient.
Synchronization Object	The left pane displays the source database objects, and the right pane displays the selected objects. You can select Tables, Import object file, or Databases for Synchronization Object as required. Database-level synchronization: In full synchronization, the selected databases and the inventory data of the database objects are synchronized. In incremental synchronization, the DML and some DDL statements of all tables except unlogged tables and temporary tables are synchronized. Table-level synchronization: In full synchronization, the inventory data of the selected tables, sequences, views, or materialized views is synchronized. In incremental synchronization, the DML and some DDL statements of the selected tables are synchronized. If the synchronization objects in source and destination databases have different names, you can map the source object name to the destination one. For details, see Changing Object Names (Mapping Object Names). When a schema name or table name is mapped, to prevent conflicts between indexes and constraint names, the original index name in the table is changed to the following format after synchronization: i_+hash value+original index name (which may be truncated)+_key The hash value is calculated based on the original schema name_original table name_original index name. Similarly, after the synchronization, the original constraint name on the table is changed to c_ + hash value + original constraint name (which may be truncated) + _key. 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.

From PostgreSQL to PostgreSQL