Help Center/ Data Replication Service/ Real-Time Synchronization/ Between Self-built Databases/ From PostgreSQL to GaussDB Distributed
Updated on 2024-12-01 GMT+08:00
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From PostgreSQL to GaussDB Distributed

Supported Source and Destination Databases

Table 1 Supported databases

Source DB

Destination DB
  • On-premises database (PostgreSQL 9.4, 9.5, 9.6, 10, 11, 12, 13 and 14)
  • ECS database (PostgreSQL 9.4, 9.5, 9.6, 10, 11, 12, 13 and 14)

GaussDB Distributed

Only whitelisted users can use this function.

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 2. DRS automatically checks the database account permissions in the pre-check phase and provides handling suggestions.

Table 2 Database account permissions

Type

Full Synchronization

Full+Incremental Synchronization

Source database user

The CONNECT permission for databases, the USAGE permission for schemas, the SELECT permission for tables, and the SELECT permission for sequences

The CONNECT permission for databases, the USAGE permission for schemas, the SELECT permission for tables, the SELECT permission 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.
  • To add the permission to create replication connections, perform the following steps:
    1. Add host replication <src_user_name> <drs_instance_ip>/32 <Authentication mode> before all configurations in the pg_hba.conf file of the source database.

      For details about the authentication mode, see pg_hba.conf in the official document of PostgreSQL. scram-sha-256 is a common authentication mode.

    2. Run select pg_reload_conf(); in the source database as user SUPERUSER, or restart the DB instance to apply the changes.

Destination database user

The user has the sysadmin role or the following minimum permissions:

  • The CONNECT and CREATE permissions for databases, the USAGE and CREATE permissions for schemas, and the INSERT, UPDATE, DELETE, SELECT, ALTER, INDEX, and COMMENT permissions for tables.
  • If gs_loader is used to create system catalogs (such as public.pgxc_copy_error_log and public.gs_copy_summary) in the destination database, the all privilege permission is required for accessing the system catalogs.For details, see gs_loader.
  • 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.

Supported Synchronization Objects

Table 3 lists the objects that can be synchronized in different scenarios. DRS will automatically check the objects you selected before the synchronization.

Table 3 Supported synchronization objects

Type

Precautions

Objects
  • Instance-level synchronization is not supported.

    Only one database can be synchronized at a time. To synchronize multiple databases, create multiple DRS tasks.

  • Supported field types:
    • GaussDB (PostgreSQL-compatible) data types, such as tinyint, smallint, int, bigint, real, double, bit, bit varying, boolean, bytea, numeric, decimal, char, bpchar, varchar, text, date, time, timetz, timestamp, timestamptz, interval, cidr, path, box, lseg, macaddr, point, polygon, inet, tsquery, tsvector, uuid, json and jsonb, are supported.
    • XML, line, domain, and self-built data type synchronization is not supported.
  • Scope of full synchronization
    • Supported: schemas, tables, primary key and unique constraints, table data, and sequences
    • Not supported: system schemas and system catalogs (The following schemas are system schemas in the destination database and cannot be synchronized: "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").
    • A user-defined table that has no primary key and is a partitioned table cannot be synchronized. Otherwise, data may be inconsistent or the task may fail.
    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. Only table-level synchronization is supported. Constraints on tables can be synchronized together. Common indexes, rules, and triggers of tables cannot be synchronized. Only objects in the primary table can be synchronized. All data in the partition table will be written to the primary table.
    • Schema: Permissions of the public schema are not synchronized. During table-level synchronization, the permissions of existing schemas in the destination database are synchronized.
  • Scope of incremental synchronization
    • Supported: some DML statements, including INSERT, UPDATE, and DELETE
    • Not supported: DDL statements, DML statements of unlogged tables and temporary tables
    • DML synchronization of partitioned tables: If a partition is a new one, the partition must be newly created and the partition name must be unique. This partition can be deleted from the source database only after all DML data is synchronized to the destination database.
      NOTE:

      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.)

Precautions

The full+incremental synchronization process consists of four phases: task startup, full synchronization, incremental synchronization, and task completion. 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 pg_hba.conf file of the source database contains the following configuration: 
      host replication all 0.0.0.0/0 md5

      The wal_level value of the source database must be logical.

      The test_decoding plug-in must be installed on the source database in advance.

      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:
    • The objects that have dependencies must be synchronized at the same time. Otherwise, the synchronization may fail.
      NOTE:

      Common dependencies: tables referenced by primary and foreign keys, parent tables referenced by child tables, partitioned tables referenced by sub-partitioned tables, and sequences referenced by auto-increment columns.

  • Destination database parameter requirements:
    • The max_prepared_transactions value of the destination database must be greater than that of the source database.
    • The max_worker_processes value of the destination database must be greater than that of the source database.
    • The max_locks_per_transaction value of the destination database must be greater than that of the source database.
    • The max_connections value of the destination database must be greater than that of the source database.
    • The lc_monetary value of the destination database must be the same as that of the source database.
  • Destination database object requirements:
    • The character set of the destination database must be the same as that of the source database.
    • The time zone of the destination database must be the same as that of the source database.
    • Do not use foreign keys for tables during synchronization. Otherwise, the sequence of writing data to different tables may be inconsistent with that in the source database, which may trigger foreign key constraints and cause synchronization failures.
    • 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.

  • 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.
    • Cascading one-way synchronization is not supported. For example, data cannot be synchronized from instance A to instance B and then from instance B to instance C.
    • Only the primary table can be synchronized. The primary table will be converted into a common table and synchronized to the destination database. Data in the partition table will be written to the primary table.
    • 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. If a long transaction is started in the source database, the creation of the logical replication slot will be blocked. As a result, the task fails.
    • 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.
    • In a full synchronization for the table structure, the length of the character and character varying types in the source database automatically increases by byte in the destination database (because the length of the destination database is in the unit of byte). By default, the length is increased by four times, and the maximum length is 10485760.
    • During table structure synchronization in the full phase, if there is a schema with the same name as a user in the destination database and another user is used to synchronize the table structure to the schema, run the grant [role] to [role] command to grant permissions to the user. Otherwise, the synchronization may fail because the table structure cannot be created.
    • Case conversion is not performed on names of objects after they are synchronized to the destination database.
    • If a unique index in the source database is an expression index, the destination distributed GaussDB may fail to create the index during full synchronization. As a result, the task fails.

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 during off-peak hours of the source database 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:
    • When a full+incremental synchronization task is complete, the streaming replication slot created by the task in the source database is automatically deleted.
  • Forcibly stop a task:
    • 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.
    • 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.

Procedure

  1. On the Data Synchronization Management page, click Create Synchronization Task.
  2. 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 Self-built to self-built.

      Source DB Engine

      Select PostgreSQL.

      Destination DB Engine

      Select GaussDB Distributed.

      Network Type

      Available options: Public network and VPN or Direct Connect. Public network is used as an example.

      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.

      Security Group

      Select a security group. You can use security group rules to allow or deny access to the instance.

      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

        This synchronization mode is suitable for scenarios where service interruption is acceptable. Database objects and data, including tables, views, and stored procedures, from non-system databases can be synchronized to the destination all at once.

      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.
    • AZ
      Figure 3 AZ
      Table 7 Task AZ

      Parameter

      Description

      AZ

      Select the AZ where you want to create the DRS task. Selecting the one housing the source or destination database can provide better performance.
    • Enterprise Project and Tags
      Figure 4 Enterprise Project 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.

  3. 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.

    • Network connectivity: Ensure that the source and destination databases accept connections from the IP address of 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

    IP Address or Domain Name

    The IP address or domain name of the source database.

    Port

    The port of the source database. Range: 1 – 65535

    Database Name

    Indicates whether to specify a database. If this option is enabled, enter the database name.

    Database Username

    The username for accessing the source database.

    Database Password

    The password for the database username.

    SSL Connection

    SSL encrypts the connections between the source and destination databases.
    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

    You can enter up to 10 groups of IP addresses or domain names of the destination database. Separate multiple values with commas (,). Example: 192.168.0.1:8000,192.168.0.2:8000

    Database Username

    The username for accessing the destination database.

    Database Password

    The password for the database username.

    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.

  4. On the Set Synchronization Task page, select the objects to be synchronized, and then 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 10 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 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.

    Source Database Replication Slot Name

    You can choose whether to specify the replication slot of the source database. This parameter is available for incremental tasks. After replication slot is enabled, enter the replication slot name. The name can contain a maximum of 63 characters and cannot start with a digit. Only lowercase letters, digits, and underscores (_) are allowed.

    Synchronization Object

    The left pane displays the source database objects, and the right pane displays the selected objects. You can select Tables or Import object file for Synchronization Object as required.

    • 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, 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.

  5. 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.

  6. 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.

  7. 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.