Updated on 2023-04-26 GMT+08:00

From GaussDB Distributed to Kafka

Supported Source and Destination Databases

Table 1 Supported databases

Source DB

Destination DB

GaussDB distributed

Kafka 0.11 or later

Supported Synchronization Objects

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

Table 2 Supported synchronization objects

Type

Synchronization Scope

Synchronization scope

  • Instance-level synchronization is not supported. Only one database can be synchronized at a time. To synchronize multiple databases, create multiple tasks.
  • Supported scenario: Incremental synchronization
  • Supported fields: INTEGER, TINYINT, SMALLINT, BIGINT, NUMBER, NUMERIC, REAL, DOUBLE PRECISION, CHARACTER, CHARACTER VARYING, NVARCHAR2, BIT, BIT VARYING, BLOB, BYTEA, CLOB, RAW, TEXT, JSON, BOOLEAN, DATE, SMALLDATETIME, TIME WITH TIME ZONE, TIME WITHOUT TIME ZONE, TIMESTAMP WITH TIME ZONE, TIMESTAMP WITHOUT TIME ZONE, INTERVAL, BOX, CIDR, CIRCLE, INET, LSEG, MACADDR, MONEY, PATH, POINT, POLYGON, TSQUERY, TSVECTOR, REFCURSOR, UUID and ARRAY.
  • Table-level synchronization or object file import is supported.
    • Only DML statements of the selected table can be synchronized.
    • Databases without schemas cannot be synchronized.
    • Schemas without tables cannot be synchronized.
    • Column-store tables, compressed tables, delay tables, and temporary tables cannot be synchronized. Do not synchronize unlogged tables.
    • The database name, schema name, and table name cannot contain special characters /<.>\\'`|\?! The column name cannot contain double quotation marks ("), single quotation marks ('), or periods (.).
    • If you select tables by importing an object file, ensure that the imported table exists in the source database or is visible to the synchronization user.

Database User Permission Requirements

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

  • You are advised to create an independent database account for DRS task connection to prevent task failures caused by database account password modification.
  • After changing the account passwords for the source or destination databases, modify the connection information in the DRS task as soon as possible to prevent automatic retry after a task failure. Automatic retry will lock the database accounts.
  • If a distributed database is the source database, the connectivity of each DN needs to be checked. You are advised to perform data synchronization as a non-root database user to prevent user locking due to incorrect password during DN connection.
Table 3 Database user permission

Type

Incremental

Source database user

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

The REPLICATION permission or the permission inherited from the built-in role gs_role_replication, the CONNECT permission for databases, the USAGE permission for schemas, and the SELECT permission for tables.

Suggestions

  • 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.
  • It is recommended that you start a task during off-peak hours to minimize the impact of synchronization on your services.
  • For more information about the impact of DRS on databases, see What Is the Impact of DRS on Source and Destination Databases?

Precautions

DRS incremental synchronization consists of three phases: task start, incremental synchronization, and task completion. 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:

    If incremental synchronization is selected:

    • The wal_level parameter of the source database is set to logical.
    • The enable_slot_log parameter of the source database is set to on.
    • The max_replication_slots value of the source database must be greater than the number of used replication slots.
    • Set the REPLICA IDENTITY attribute of a table without a primary key to FULL, or add a primary key to the table.
    • Set the REPLICA IDENTITY attribute of the table that has a primary key to FULL.
  • Source database object requirements:
    • The names of the source database, schema, and table to be synchronized cannot contain special characters /<.>\\'`|\?!
  • Destination database requirements:
    • The destination database is a Kafka database.
  • Other notes:
    • The source database must be a GaussDB distributed instance.
    • Before a task enters the incremental synchronization phase, ensure that long-running transactions are not started in the source database. Starting the long transaction will block the creation of the logical replication slot and cause the task to fail.
    • If a logical replication slot fails to be created or does not exist due to a long transaction, you can reset the task and then restart it.

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 REPLICA IDENTITY value of a table in the source database. Otherwise, incremental data may be inconsistent or the task may fail.
  • During synchronization of table-level objects, renaming tables is not recommended.
  • Replication of interval partition tables is not supported.
  • The name of a primary key column cannot be changed.
  • After a DDL statement is executed in a transaction, the DDL statement and subsequent statements are not synchronized.
  • Logical log decoding is restricted by the decoding capability of the GaussDB kernel. For details about the restrictions, see the precautions in "Logical Decoding" of GaussDB Developer Guide.

Stopping a task

  • Stop a task normally:
    • When an incremental synchronization task is complete, the streaming replication slot created by the task in the source database is automatically deleted.

Prerequisites

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

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 and recipient description

      Parameter

      Description

      Region

      The region where the synchronization instance is deployed. You can change the region.

      Project

      The project corresponds to the current region and can be changed.

      Task Name

      The task name must start with a letter and consist of 4 to 50 characters. It can contain only letters, digits, hyphens (-), and underscores (_).

      Description

      The description consists of a maximum of 256 characters and cannot contain special characters !=<>'&"\

    • Synchronization instance details
      Figure 2 Synchronization instance details
      Table 6 Synchronization instance settings

      Parameter

      Description

      Data Flow

      Choose Self-built to self-built.

      Source DB Engine

      Select GaussDB Distributed.

      Destination DB Engine

      Select Kafka.

      Network Type

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

      VPC

      Select an available VPC.

      Synchronization Instance Subnet

      Select the subnet where the synchronization instance is located. You can also click View Subnet 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 ensure that there are available IP addresses. 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

      • Incremental

        Through log parsing, incremental data generated on the source database is synchronized to the destination database.

        During synchronization, the source database continues to provide services for external systems with zero downtime.

      AZ

      Select the AZ where you want to create the DRS instance. Selecting the one housing the source or destination database can provide better performance.

      Source Shard Quantity

      The value must be the same as the number of DNs in the distributed source database. Run the following SQL statement to check the value of Source Shard Quantity:

      SELECT count(DISTINCT node_name) FROM pgxc_node WHERE node_type = 'D';
    • DRS instance specifications
      Figure 3 Specifications
      Table 7 Specifications

      Parameter

      Description

      Specifications

      DRS instance specifications. Different specifications have different performance upper limits. For details, see Real-Time Synchronization.

      NOTE:

      Currently, DRS supports specification upgrade only in MySQL-to-MySQL synchronization tasks with single-node DRS instances configured. Task specifications cannot be downgraded. For details, see Changing Specifications.

    • Enterprise Projects and Tags
      Figure 4 Enterprise projects and tags
      Table 8 Enterprise Projects and Tags

      Parameter

      Description

      Enterprise Project

      An enterprise project you would like to use to centrally manage your Global Accelerator resources. 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 Management page is displayed. For details, see Creating an Enterprise Project in Enterprise Management User Guide.

      Tags

      • This setting is optional. Adding tags helps you better identify and manage your tasks. Each task can have up to 10 tags.
      • 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 ends.

  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, click Next.

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

    • Network connectivity: Ensure that the source and destination databases accept connections from the DRS instance. To access databases over a public network, configure the database to accept connections from the EIP of the DRS instance. To access databases over a VPC, VPN, or Direct Connect network, configure the database to accept connections from the private IP address of the DRS instance. For details, see Network Preparations.
    • Account connectivity: Ensure that the source and destination databases allows connections from the DRS instance using the username and password.
    Figure 5 Source database information
    Table 9 Source database settings

    Parameter

    Description

    CN IP Address or Domain Name

    Enter the IP addresses of GaussDB. Ensure that the entered IP addresses or domain names belong to the same instance.

    Database Username

    The username for accessing the source database.

    Database Password

    The password for the database username.

    DN IP Address or Domain Name

    You can log in to the CN and run the following SQL statement to query the DN IP address:

    SELECT node_name as dn_name, string_agg(node_host || ':' || node_port, ',' order by node_type) AS dn_ip FROM pgxc_node WHERE node_type != 'C' GROUP BY node_name;

    The resource types of different database instances are different. Therefore, you are advised to contact O&M personnel.

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

    Figure 6 Destination database information
    Table 10 Destination database settings

    Parameter

    Description

    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 (,). For example: 192.168.0.1:8080,192.168.0.2:8080.

    Connection Method

    Available options: PLAINTEXT, SSL, SASL_PLAINTEXT, and SASL_SSL. For details, see Kafka Authentication.

  4. On the Set Synchronization Task page, select the synchronization policy, objects, and data format, and click Next.

    Figure 7 Synchronization mode
    Table 11 Synchronization object

    Parameter

    Description

    Source Database Replication Slot Name

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

    Topic Synchronization Policy

    Topic synchronization policy. You can select A specific topic or Auto-generated topics.

    Topic

    Select the topic to be synchronized to the destination database. This parameter is available when Topic Synchronization Policy is set to A specified topic.

    Topic Name Format

    This parameter is available when Topic Synchronization Policy is set to Auto-generated topics.

    Due to Kafka restrictions, a topic name can contain only ASCII characters, periods (.), underscores (_), and hyphens (-). If a topic name exceeds the limit, the topic fails to be created and the task is abnormal.

    If a topic name contains a database object name, ensure that the characters in the object name meet the Kafka topic naming requirements.

    Number of Partitions

    This parameter is available when Topic Synchronization Policy is set to Auto-generated topics.

    The number of partitions of a topic. Each topic can have multiple partitions. More partitions can provide higher throughput but consume more resources. Set the number of partitions based on the actual situation of brokers.

    Replication Factor

    This parameter is available when Topic Synchronization Policy is set to Auto-generated topics.

    Number of copies of a topic. Each topic can have multiple copies, and the copies are placed on different brokers in a cluster. The number of copies cannot exceed the number of brokers. Otherwise, the topic fails to be created.

    Synchronize Topic To

    The policy for synchronizing topics to the Kafka partitions.

    • If topics are synchronized to different partitions by hash value of the database, schema and table names, the performance on a single table query can be improved.
    • If topics are synchronized to different partitions by hash value of the primary key, one table corresponds to one topic. This prevents data from being written to the same partition, and consumers can obtain data from different partitions concurrently.

      For a table without a primary key, if you select Partitions are identified by the hash values of the primary key, topics are synchronized to different partitions based on the hash value of the database_name.schema.table_name.

    • Partitions are differentiated by the hash values of database_name.schema_name: This mode applies to scenarios where one database corresponds to one topic, preventing multiple schemas from being written to the same partition, so that consumers can obtain data from different partitions concurrently.
    • If topics are synchronized to partition 0, strong consistency can be obtained but write performance is impacted.

    Data Format in Kafka

    Select the data format to be delivered to Kafka.

    • Avro refers to binary encoded format.
    • JSON: JSON message format, which is easy to interpret but takes up more space.

    For details, see Kafka Message Format.

    Synchronization Object

    The left pane displays the source database objects, and the right pane displays the selected objects. DRS supports table-level synchronization. You can select data for synchronization based on your service requirements.

    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 the object name contains spaces, the spaces before and after the object name are not displayed. If there are multiple spaces between the object name and 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 Checking Whether the Source Database Is Connected in Data Replication Service User Guide.

    • If all check items are successful, click Next.
      Figure 8 Pre-check

      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 Notification, SMN Topic, Synchronization Delay Threshold, 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

    Started 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

    SMN topic. This parameter is optional. If an exception occurs during synchronization, the system will send a notification to the specified recipients.

    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.

    Synchronization Delay Threshold

    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 Notification.

    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:

    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, and the task status remains unchanged. When you restart the task configuration, DRS applies for resources again.