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- What's New
- Product Bulletin
- Service Overview
- Billing
- Getting Started
-
User Guide
- Function Overview
- Kernel Version Notes
- Permissions Management
-
Instance Management
- Instance Statuses
- Buying a DDM instance
- Splitting Read-only and Read-Write Services
- Changing Node Class
- Scaling Out a DDM Instance
- Scaling In a DDM Instance
- Restarting a DDM Instance or an Instance Node
- Deleting Pay-per-Use Instances
- Reloading Table Data
- Changing a Parameter Template
- Modifying Parameters of a DDM Instance
- Rolling Back the Version of a DDM Instance
- Upgrading the Version of a DDM Instance
- Upgrading the DDM Engine and OS
- Connection Management
- Schema Management
- Shard Configuration
- Data Nodes
-
Parameter Template Management
- Instance Parameters
- Creating a Parameter Template
- Modifying a Custom Parameter Template
- Comparing Two Parameter Templates
- Viewing Parameter Change History
- Replicating a Parameter Template
- Applying a Parameter Template
- Viewing Application Records of a Parameter Template
- Modifying the Description of a Parameter Template
- Deleting a Parameter Template
- Account Management
- Backups and Restorations
-
Data Migration
- Overview
- Migration Evaluation
- Scenario 1: Migrating Data from an On-Premises MySQL Instance to DDM
- Scenario 2: Migrating Data from a Third-Party Cloud MySQL Instance to DDM
- Scenario 3: Migrating Data from an ECS-hosted MySQL Instance on Huawei Cloud to DDM
- Scenario 4: Exporting Data from a DDM Instance
- Scenario 5: Migrating Data from Heterogeneous Databases to DDM
- Scenario 6: Migrating Data from Huawei Cloud RDS for MySQL to DDM
- Session Management
- Slow Queries
- Monitoring and Alarm Reporting
- Task Center
- Tags
- Auditing
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SQL Syntax
- Introduction
- DDL
- DML
- Online DDL
- Functions
- Unsupported Objects and Use Constraints
- Supported SQL Statements
- Global Sequence
- Database Management Syntax
- Advanced SQL Functions
- Quotas
-
API Reference
- Before You Start
- API Overview
- Calling APIs
-
APIs (Recommended)
-
DDM Instances
- Buying a DDM instance
- Querying DDM Instances
- Querying Details of a DDM Instance
- Modifying the Name of a DDM Instance
- Changing the Security Group of a DDM Instance
- Deleting a DDM Instance
- Restarting a DDM Instance
- Reloading Table Data
- Scaling Out a DDM Instance
- Scaling in a DDM instance
- Modifying the Read Policy of the Associated DB Instance
- Synchronizing Data Node Information
- Querying Nodes of a DDM Instance
- Querying Details of a DDM Instance Node
- Querying Parameters of a Specified DDM Instance
- Modifying Parameters of a DDM Instance
- Querying DDM Engine Information
- Querying DDM Node Classes Available in an AZ
- Changing the Node Class of a DDM Instance
- Obtaining the Instance Group Information
- Creating an Instance Group
- Schemas
- Accounts
- Monitoring
- Session Management
- Application Examples
-
DDM Instances
- Permissions Policies and Supported Actions
- Appendix
- SDK Reference
-
Best Practices
- Overview
- Formulating Sharding Rules
- Determining the Number of Shards in a Schema
- Using Broadcast and Unsharded Tables
- Transaction Models
- SQL Standards
- Migrating an Entire RDS Database to DDM
- Migrating an Entire MyCat Database to DDM
- Accessing DDM Using a JDBC Connection Pool
- Logging In to a DDM Instance Using Navicat
- Migrating Data from RDS for MySQL to DDM Using DRS
- Sharding Database and Table Data of an RDS for MySQL Instance
- Performance White Paper
-
FAQs
- General Questions
-
DDM Usage
- How Does DDM Perform Sharding?
- What Do I Do If I Fail to Connect to a DDM Instance Using the JDBC Driver?
- Why It Takes So Long Time to Export Data from MySQL Using mysqldump?
- What Do I Do If a Duplicate Primary Key Error Occurs When Data Is Imported into DDM?
- What Should I Do If an Error Message Is Returned When I Specify an Auto-Increment Primary Key During Migration?
- What Do I Do If an Error Is Reported When Parameter Configuration Does Not Time Out?
- Which Should I Delete First, a Schema or its Associated RDS Instances?
- Can I Manually Delete Databases and Accounts Remained in Data Nodes After a Schema Is Deleted?
- SQL Syntax
-
RDS-related Questions
- Is the Name of a Database Table Case-Sensitive?
- What Risky Operations on RDS for MySQL Will Affect DDM?
- How Do I Handle Data with Duplicate Primary Keys in a Table?
- How Can I Query RDS for MySQL Information by Running Command show full innodb status?
- What Should I Pay Attention to When Selecting RDS for MySQL Instance Specifications?
- Connection Management
- Resource Freezing, Release, Deletion, and Unsubscription
- Videos
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More Documents
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User Guide (ME-Abu Dhabi Region)
- Service Overview
- Getting Started
- Function Overview
- Instance Management
-
Parameter Template Management
- Creating a Parameter Template
- Editing a Parameter Template
- Comparing Two Parameter Templates
- Viewing Parameter Change History
- Replicating a Parameter Template
- Applying a Parameter Template
- Viewing Application Records of a Parameter Template
- Modifying the Description of a Parameter Template
- Deleting a Parameter Template
- Task Center
- Schema Management
- Account Management
- Backup Management
- Monitoring Management
- Auditing
-
SQL Syntax
- Introduction
- DDL
- DML
- Functions
- Unsupported Items
- Supported SQL Statements
- Global Sequence
- Database Management Syntax
- Advanced SQL Functions
-
FAQs
- General Questions
-
DDM Usage
- How Can I Rectify a Fault in Accessing DDM by Using the JDBC Driver?
- What Version and Parameters Should I Select?
- Why It Takes So Long Time to Export Data from MySQL Using mysqldump?
- How Should I Handle the Duplicate Primary Key Error Occurring After Data Is Imported into DDM?
- What Should I Do If an Error Message Is Returned After I Specify an Auto-Increment Primary Key?
- How Do I Handle the Error Reported When Parameter Configuration Does Not Time Out?
- Which Should I Delete First, Schema or Associated RDS DB Instances?
- Should I Manually Delete Databases and Accounts Remained in the Associated RDS DB Instances After a Schema Is Deleted?
- SQL Syntax
- RDS-related Questions
- Connection Management
-
User Guide (Kuala Lumpur Region)
- Service Overview
- Getting Started
- Function Overview
- Instance Management
-
Parameter Template Management
- Creating a Parameter Template
- Editing a Parameter Template
- Comparing Two Parameter Templates
- Viewing Parameter Change History
- Replicating a Parameter Template
- Applying a Parameter Template
- Viewing Application Records of a Parameter Template
- Modifying the Description of a Parameter Template
- Deleting a Parameter Template
- Task Center
- Schema Management
- Account Management
- Backup Management
- Monitoring Management
- Auditing
-
SQL Syntax
- Introduction
- DDL
- DML
- Functions
- Unsupported Items
- Supported SQL Statements
- Global Sequence
- Database Management Syntax
- Advanced SQL Functions
-
FAQs
- General Questions
-
DDM Usage
- How Can I Rectify a Fault in Accessing DDM by Using the JDBC Driver?
- What Version and Parameters Should I Select?
- Why It Takes So Long Time to Export Data from MySQL Using mysqldump?
- How Should I Handle the Duplicate Primary Key Error Occurring After Data Is Imported into DDM?
- What Should I Do If an Error Message Is Returned After I Specify an Auto-Increment Primary Key?
- How Do I Handle the Error Reported When Parameter Configuration Does Not Time Out?
- Which Should I Delete First, Schema or Associated RDS DB Instances?
- Should I Manually Delete Databases and Accounts Remained in the Associated RDS DB Instances After a Schema Is Deleted?
- SQL Syntax
- RDS-related Questions
- Connection Management
-
API Reference (Kuala Lumpur Region)
- Before You Start
- API Overview
- Calling APIs
-
DDM Instance Management
- Querying DDM Engine
- Querying the Quota of Classes Available in Each AZ
- Creating a DDM Instance
- Querying DDM Instances
- Viewing Details of a DDM Instance
- Modifying the Name of a DDM Instance
- Modifying the Security Group of a DDM Instance
- Deleting a DDM Instance
- Restarting a DDM Instance
- Reloading Table Data
- Scaling Out a DDM instance
- Scaling In a DDM instance
- Modifying the Read Policy of the Associated DB Instance
- Synchronizing DB Instance Data
- Querying Nodes of a DDM Instance
- Querying Details of a DDM Instance Node
- Querying Parameters of a Specified DDM Instance
- Modifying Parameters of a DDM Instance
- Schema Management
- Account Management
- Monitoring Management
- Permissions Policies and Supported Actions
- Appendix
- Change History
-
User Guide (ME-Abu Dhabi Region)
- General Reference
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Configuring Read/Write Splitting
Read/Write splitting offloads read requests from associated primary DB instances to its read replicas at a ratio, improving processing of read/write transactions. This function is transparent to applications, and you do not need to modify service code. Configure read weights of primary instances and their read replicas on the DDM console, and read traffic will be distributed at the preset ratio and write traffic will be forwarded to the primary instances by default. The ratio is generally based on service requirements and loads of associated data nodes.
Data is asynchronously replicated from the primary instance to read replicas, and there is a delay between them in milliseconds. Set weights of the primary instance and its read replicas to 0 and 100, respectively, that is, distribute all read requests to read replicas if sub-second latency is allowed for read requests and these requests require high query costs that may impact read/write transactions. In other scenarios, adjust the ratio based on service requirements.
Precautions
- If the DDM kernel version is 3.1.0 or later, you need to manually enable read/write splitting and then adjust read weights of your primary instance and read replicas.
- If the DDM kernel version is earlier than 3.1.0, read/write splitting is enabled by default. You just need to adjust read weights of your primary instance and read replicas.
- The SELECT statements that contain hints or modify data in transactions are all executed by the primary instance.
- If the primary instance becomes faulty and parameter Seconds_Behind_Master on its read replicas is set to NULL, read-only requests are still forwarded to the primary instance. Recover the faulty instance as soon as possible.
Prerequisites
- You have bought a DDM instance and a data node with read replicas.
- You have created a schema.
Procedure
- Log in to the DDM console.
- Locate the DDM instance that you want to configure read/write splitting for and click its name.
- In the navigation pane on the left, choose Data Nodes.
- Enabling read/write splitting affects only the nodes in read/write groups.
- If the DDM kernel version is 3.1.0 or later, you need to manually enable read/write splitting by referring to Enabling Read/Write Splitting. Then, go to 5.
- If the kernel version is earlier than 3.1.0, read/write splitting is enabled by default. Skip this step and go to 5.
NOTE:
You can create a read-only group and use the private IP address of the read-only group to process read requests without enabling read/write splitting. For details, see Creating a Read-Only Group.
- Configure read weights.
For details, see Configuring Read Weights.
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