Help Center/ TaurusDB/ User Guide/ RegionlessDB Clusters/ Using a RegionlessDB Cluster for Remote Multi-Active DR
Updated on 2024-11-06 GMT+08:00
View PDF
Share

Using a RegionlessDB Cluster for Remote Multi-Active DR

Scenarios

If your workloads are deployed in multiple regions, you can create a RegionlessDB cluster to access databases from the nearest region. As shown in Figure 1, a RegionlessDB cluster contain a primary instance and two standby instances. Read requests are sent to a standby instance in the nearest region, and write requests are automatically forwarded from the nearest region to the primary instance. After data is written to the primary instance, the data is synchronized to all standby instances, reducing the cross-region network latency.

Figure 1 Remote multi-active principle

Constraints

For details, see Constraints.

Procedure

Step 1: Create a RegionlessDB Cluster

  1. Log in to the management console.
  2. Click in the upper left corner and select a region and project.
  3. Click in the upper left corner of the page and choose Databases > GaussDB(for MySQL).
  4. On the RegionlessDB page, click Create RegionlessDB in the upper right corner.
    Figure 2 Creating a RegionlessDB cluster

  5. In the Create RegionlessDB dialog box, configure RegionlessDB Name, Primary Instance Region, and Primary Instance.
    Figure 3 Configuring the RegionlessDB cluster information

    Table 1 Parameter description

    Parameter

    Description

    RegionlessDB Name

    The name must start with a letter and consist of 4 to 64 characters. Only letters (case-sensitive), digits, hyphens (-), and underscores (_) are allowed.

    Primary Instance Region

    Select a region where the primary instance is located.

    Primary Instance

    Select an existing DB instance as the primary instance of the RegionlessDB cluster.
  6. Click OK.
  7. After the primary instance is created, view and manage it.

    During the creation process, the instance status is Creating. To view the detailed progress and result of the creation, go to the Task Center page. After the status of the primary instance is Available, you can use the instance.

Step 2: Add a Standby Instance

  1. On the RegionlessDB page, locate the RegionlessDB cluster.
  2. Click Add Standby Instance in the Operation column.
    Figure 4 Adding a standby instance

  3. On the displayed page, configure related parameters.
    Table 2 Basic information

    Parameter

    Description

    Region

    Region where the standby instance is deployed.

    NOTICE:

    Products in different regions cannot communicate with each other through a private network. After a DB instance is purchased, the region cannot be changed.

    Creation Method

    Create new

    DB Instance Name

    The name must start with a letter and consist of 4 to 64 characters. Only letters, digits, hyphens (-), and underscores (_) are allowed.

    DB Engine

    GaussDB(for MySQL)

    DB Engine Version

    MySQL 8.0

    Kernel Version

    Kernel version of the standby instance. The kernel version must be 2.0.46.231000 or later.

    For details about the updates in each minor kernel version, see Kernel Version Release History.

    NOTE:

    To configure the kernel version, contact customer service.

    DB Instance Type

    Only Primary/Standby can be selected. There are 2 to 10 read replicas in a primary/standby instance in the RegionlessDB cluster.

    Storage Type

    Shared

    AZ Type

    An AZ is a physical region where resources have their own independent power supply and networks. AZs are physically isolated but interconnected through an internal network. Some regions support both single-AZ and multi-AZ deployment and some only support single-AZ deployment.

    • Single AZ: The primary node and read replicas are deployed in the same AZ.
    • Multi-AZ: The primary node and read replicas are deployed in different AZs to ensure high reliability.

    Time Zone

    You need to select a time zone for your instance based on the region hosting your instance. The time zone is selected during instance creation and cannot be changed after the instance is created.

    Instance Specifications

    For details about the specifications supported by GaussDB(for MySQL), see Instance Specifications.

    GaussDB(for MySQL) is a cloud-native database that uses the shared storage. To ensure service stability in high read/write pressure, the system controls the read/write peaks of DB instances based on instance specifications. For details about how to select specifications, see Performance White Paper.

    CPU Architecture

    The CPU architecture can be x86 or Kunpeng. Under a CPU architecture, you need to select vCPUs and memory of the instance.

    Nodes

    All nodes of the standby instance are read replicas. You can apply for a maximum of 10 read replicas at a time for a pay-per-use instance.

    After an instance is created, you can add read replicas as required. Up to 15 read replicas can be created for a standby instance in a cluster.

    Storage

    Storage will be scaled up dynamically based on the amount of data that needs to be stored, and is billed hourly on a pay-per-use basis.

    VPC
    • A dedicated virtual network in which your GaussDB(for MySQL) instance is located. It isolates networks for different workloads. You can select an existing VPC or create a VPC. For details about how to create a VPC, see Creating a VPC.

      If no VPC is available, GaussDB(for MySQL) allocates a VPC to you by default.

      NOTICE:
      • Ensure that the VPC selected for the standby instance is connected to the VPC selected for the primary instance through a VPN.
      • After a GaussDB(for MySQL) instance is created, the VPC cannot be changed.
    • A subnet provides dedicated network resources that are logically isolated from other networks for network security.

      A private IP address is automatically assigned when you create a DB instance. You can also enter an idle private IP address in the subnet CIDR block.

    Security Group

    It can enhance security by controlling access to GaussDB(for MySQL) from other services. When you select a security group, you must ensure that it allows the client to access instances.

    If no security group is available or has been created, GaussDB(for MySQL) allocates a security group to you by default.

    NOTE:
    • To ensure subsequent database connection and access, you need to allow all IP addresses to access your DB instance through port 3306 and over ICMP.
    • Configure private network security group rules to ensure that the primary and standby instances in a cluster can communicate with each other.

    Parameter Template

    Contains engine configuration values that can be applied to one or more instances. You can modify the instance parameters as required after the instance is created.

    NOTICE:

    If you use a custom parameter template when creating a DB instance, the following specification-related parameters in the custom template are not applied. Instead, the default values are used.

    innodb_buffer_pool_size

    innodb_log_buffer_size

    max_connections

    innodb_buffer_pool_instances

    innodb_page_cleaners

    innodb_parallel_read_threads

    innodb_read_io_threads

    innodb_write_io_threads

    threadpool_size

    After a DB instance is created, you can adjust its parameters as needed. For details, see Modifying Parameters in a Parameter Template.

    Enterprise Project

    Only available for enterprise users. If you want to use this function, contact customer service.

    An enterprise project provides a way to manage cloud resources and enterprise members on a project-by-project basis.

    You can select an enterprise project from the drop-down list. The default project is default.

    Tag

    This parameter is optional. Adding tags helps you better identify and manage your DB instances. Each DB instance can have up to 20 tags.

    After a DB instance is created, you can view its tag details on the Tags tab. For details, see Managing Tags.

    The instance password and table name case sensitivity are the same as those of the primary instance. You do not need to set them separately.

  4. Click Next.
  5. Confirm the information and click Submit.
  6. Go to the Instances page to view and manage the instance.

    During the creation process, the instance status is Creating. To view the detailed progress and result of the creation, go to the Task Center page. After the status of the instance is Available, you can use the instance.

    If there is a large amount of data in the primary instance, it may take a long time to complete a full backup during standby instance creation.

Step 3: Enable Write Forwarding

In normal cases, after a RegionlessDB cluster is created, the primary instance receives and processes read and write requests, and standby instances receive only read requests. After write forwarding is enabled, standby instances can receive write requests and then forward them to the primary instance for processing. After data is written to the primary instance, the data is synchronized to all standby instances. Write forwarding simplifies the data write process. You can directly connect a database service through a standby instance's IP address to perform read and write operations. In addition, consistency is ensured and the nearby read is not affected.

  • Write forwarding is only available when the transaction isolation level of the standby instances is RR.
  • In the current version, WARNING and RECORD information cannot be displayed when a standby instance forwards write requests.
  • In the current version, SQL requests that are being executed cannot be interrupted when a standby instance forwards write requests.
  • When write forwarding is enabled, user _@gdb_WriteForward@_ is created. Do not modify or delete the user, or write forwarding cannot run properly.
  • The following commands are supported for write forwarding:
    • SQLCOM_UPDATE
    • SQLCOM_INSERT
    • SQLCOM_DELETE
    • SQLCOM_INSERT_SELECT
    • SQLCOM_REPLACE
    • SQLCOM_REPLACE_SELECT
    • SQLCOM_DELETE_MULTI
    • SQLCOM_UPDATE_MULTI
    • SQLCOM_ROLLBACK
    If an unsupported command is executed, the following error information is displayed. 
    ERROR xxx (yyy): This version of MySQL doesn't yet support 'operation with write forwarding'.

    operation indicates the operation type that is not supported.

  • The following scenarios are not supported:
    • There are SELECT FOR UPDATE statements.
    • There are EXPLAIN write forwarding statements.
    • The statements for write forwarding contain SET VARIABLE.
    • SAVEPOINT is not supported when write forwarding is enabled.
    • Write forwarding is not supported in XA transactions.
    • Currently, START TRANSACTION READ WRITE is not supported. You can directly use START TRANSACTION to test write forwarding.
    • Write forwarding is not supported in stored procedures.
    • When write forwarding is enabled, temporary tables cannot be created. To create temporary tables, disable write forwarding temporarily.
  • For commands that can be implicitly committed, if write forwarding is not supported, the transactions corresponding to the current node and primary node are automatically committed.
  • For the global consistency level, before accessing data for the first time, each transaction needs to use a connection in the session pool to obtain a data point (LSN) from the primary node. If no sessions are available, the command for reading data may fail.
  • If there is a connection error when a user uses a session for write forwarding and the user is in a multi-statement transaction, the server proactively closes the connections to the client and the primary node, ensuring that the client can detect the error.
  • The versions of the primary and standby instances must be the latest.
  • Write operations are finally forwarded to and processed by the primary node. If a temporary table with the same name exists in the given database of the primary and read replicas, the data on the primary node is used.
  • If there is a primary/standby switchover or failover for a standby instance in a RegionlessDB cluster, the write forwarding parameters (rds_open_write_forwarding and rds_write_forward_read_consistency) are restored to the default values.
  1. On the RegionlessDB page, locate the RegionlessDB cluster.
  2. Click Set Write Forwarding in the Operation column to create a write forwarding account.

    Figure 5 Creating a write forwarding account

    The system automatically creates an internal account (_@gdb_WriteForward@_) so that write requests can be forwarded to the primary instance for processing. You cannot modify or delete the internal account, or write forwarding will be affected.

  3. In the Set Write Forwarding dialog box, confirm the information and click OK.

    Figure 6 Setting write forwarding

  4. On the Instances page, click the name of the standby instance in the RegionlessDB cluster.
  5. In the navigation pane, choose Parameters.
  6. Search for rds_open_write_forwarding in the upper right corner of the Parameters page and change its value to ON.
  7. Click Save in the upper left corner to enable write forwarding.
  8. Search for rds_write_forward_read_consistency in the upper right corner of the Parameters page and change the read consistency level of write forwarding.

    You can modify the parameters to set the read consistency range. For details, see Table 3.

    Table 3 Parameter description

    Parameter

    Description

    NONE

    Write forwarding is disabled.

    EVENTUAL

    Results of write operations are not visible until the write operations are performed on the primary instance. The query does not wait for data synchronization between primary and standby instances to complete, so data that is not updated may be read.

    SESSION

    All queries executed by a standby instance with write forwarding enabled see the results of all data writes performed in this session. The queries wait for the results of forwarded write operations to be replicated.

    GLOBAL

    A session can view all committed changes of all sessions and instances in a RegionlessDB cluster. The query may wait for a certain period, which is related to the replication latency.
    • If read consistency is required, you are advised to set the consistency level to SESSION. The consistency level GLOBAL will cause a large extra cost for all read requests. For example, if any client is used to connect to GaussDB(for MySQL) and the GLOBAL level is used, the time for accessing the MySQL command line is prolonged.
    • The read consistency level in write forwarding cannot be changed to SESSION in a transaction.
    • Before enabling write forwarding, ensure that the transaction isolation levels of standby instances are RR.
    • When write forwarding is enabled, the transaction isolation level of the current session cannot be changed.
    • The read consistency level cannot be changed in a transaction.

  9. Click Save in the upper left corner.

Step 4: Connect to the RegionlessDB Cluster for Service Management

After a RegionlessDB cluster is created, no unified connection address is provided. The primary and standby instances in the RegionlessDB cluster provide independent connection addresses. You can use the nearest primary or standby instance based on the service access region to connect to the RegionlessDB cluster. The RegionlessDB cluster automatically forwards write requests to the primary instance for processing and read requests to the instance of the nearest region for processing.

Example:
  1. Connect to the primary instance and write data to the database. 
    mysql> CREATE DATABASE mydatabase;
mysql> CREATE TABLE orders (order_id INT PRIMARY KEY, customer_name VARCHAR(255), order_date DATE);
mysql> INSERT INTO orders (order_id, customer_name, order_date) VALUES (1, 'UserA', '2023-12-18'), (2, 'UserB', '2023-12-17'), (3, 'UserC', '2023-12-16');
  2. Use the nearest standby instance to access the database and query the data written in 1. 
    mysql> select * from mydatabase.orders;
+----------+---------------+------------+
| order_id | customer_name | order_date |
+----------+---------------+------------+
|        1 | UserA         | 2023-12-18 |
|        2 | UserB         | 2023-12-17 |
|        3 | UserC         | 2023-12-16 |
+----------+---------------+------------+
  3. Connect to database through the primary instance and run the following SQL statements to create the mydatabase database and orders table. 
    mysql> CREATE DATABASE mydatabase;
Query OK, 1 row affected (0.00 sec)
mysql> USE mydatabase;
Database changed
mysql> CREATE TABLE orders (order_id INT PRIMARY KEY, customer_name VARCHAR(255), order_date DATE);
Query OK, 0 rows affected (0.01 sec)
  4. Connect to the database from a standby instance, run the following SQL statements to write three data records to the orders table, and query the written data. 
    mysql> INSERT INTO orders (order_id, customer_name, order_date) VALUES (1, 'UserA', '2023-12-18'), (2, 'UserB', '2023-12-17'), (3, 'UserC', '2023-12-16');
Query OK, 3 rows affected (0.00 sec)
mysql> SELECT * FROM mydatabase.orders;
+----------+---------------+------------+
| order_id | customer_name | order_date |
+----------+---------------+------------+
|        1 | UserA         | 2023-12-18 |
|        2 | UserB         | 2023-12-17 |
|        3 | UserC         | 2023-12-16 |
+----------+---------------+------------+
3 rows in set (0.01 sec)
  5. Connect to the database through the primary instance and run the following SQL statements to query the data inserted by the standby instance in 4. 
    mysql> SELECT * FROM mydatabase.orders;
+----------+---------------+------------+
| order_id | customer_name | order_date |
+----------+---------------+------------+
|        1 | UserA         | 2023-12-18 |
|        2 | UserB         | 2023-12-17 |
|        3 | UserC         | 2023-12-16 |
+----------+---------------+------------+
3 rows in set (0.00 sec)
Parent Topic: RegionlessDB Clusters