Cette page n'est pas encore disponible dans votre langue. Nous nous efforçons d'ajouter d'autres langues. Nous vous remercions de votre compréhension.
- What's New
- Function Overview
- Service Overview
-
Getting Started
- Overview
- Getting Started with Clusters
- Getting Started with Replica Sets
- Getting Started with Single Nodes
- Logging In to the DDS Console
- Example: Buying and Connecting to a DDS Instance
- Change History (Getting Started) Europe Site
-
User Guide
- Migrating Data
- Performance Tuning
- Permissions Management
- Instance Lifecycle Management
- Instance Modifications
- Data Backups
- Data Restorations
-
Parameter Template Management
- Overview
- Creating a Parameter Template
- Modifying a Parameter Template
- Viewing Parameter Change History
- Exporting a Parameter Template
- Comparing Parameter Templates
- Replicating a Parameter Template
- Resetting 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
- Connection Management
- Database Usage
- Data Security
- Monitoring and Alarm Reporting
- Auditing
- Logs
- Task Center
- Billing
- Tags
- Quotas
- DDS Usage Suggestions
- Change History
- Developer Guide
-
Best Practices
- Overview
- Common Methods for Connecting to a DDS Instance
- How Do Replica Sets Achieve High Availability and Read/Write Splitting?
- Sharding
- How Do I Improve DDS Performance by Optimizing SQL Statements?
- How Do I Prevent the Mongos Cache Problem?
- How Do I Solve the High CPU Usage Issue?
- Creating a User and Granting the Read-Only Permission to the User
- Security White Paper
- Performance White Paper
-
API Reference
- Before You Start
- API Overview
- Calling APIs
- Getting Started
-
APIs V3.0 (Recommended)
- Querying the API Version
- Querying Database Version Information
- Querying Database Specifications
- Querying the Database Disk Type
-
DB Instance Management
- Creating a DB Instance
- Restarting a DB Instance
- Deleting a DB Instance
- Querying Instances and Details
- Scaling Up Storage Space
- Adding Nodes for a Cluster Instance
- Modifying DB Instance Specifications
- Performing a Primary/Secondary Switchover in a Replica Set Instance
- Enabling or Disabling SSL
- Modifying a DB Instance Name
- Changing an Instance Description
- Changing a Database Port
- Changing a Security Group
- Binding an EIP
- Unbinding an EIP
- Changing a Private IP Address
- Creating Shard or Config IP Addresses of a Cluster Instance
- Configuring Cross-CIDR Access for a Replica Set
- Querying AZs to Which an Instance Can Be Migrated
- Migrating a DB Instance to Another AZ
- Adding Nodes to a Replica Set Instance
- Adding a Read Replica to an Instance
- Connection Management
-
Backup and Restoration
- Creating a Manual Backup
- Deleting a Manual Backup
- Querying the Backup List
- Querying an Automated Backup Policy
- Setting an Automated Backup Policy
- Restoring Data to a New DB Instance
- Obtaining the Link for Downloading a Backup File
- Querying the Restoration Time Ranges
- Obtaining the List of Databases That Can Be Restored
- Obtaining the List of Database Collections That Can Be Restored
- Restoring Data to the Original DB Instance
- Restoring Databases and Tables to a Point in Time
- Parameter Configuration
- Log Information Queries
- Tag Management
-
Managing Databases and Users
- Creating a Database User
- Creating a Database Role
- Querying Details About Database Users
- Querying the Database Role List
- Changing the Password of a Database User
- Checking the Password for Logging In to a Database
- Querying Cluster Balancing Settings
- Enabling or Disabling Cluster Balancing
- Setting the Activity Time Window for Cluster Balancing
- Deleting a Database User
- Deleting a Database Role
- Quota Management
- Task Management
- API V3 (Unavailable Soon)
- Examples
- Permissions Policies and Supported Actions
- Appendix
- Change History (European Sites)
- SDK Reference
-
FAQs
-
Product Consulting
- What Is the Relationship Between DDS and MongoDB Community Edition?
- What Are the Differences Between DDS and GaussDB(for Mongo)?
- What Precautions Should Be Taken When Using DDS?
- What Is the Availability of DDS DB Instances?
- Will My DDS DB Instances Be Affected by Other Users' DDS DB Instances?
- Does DDS Support Multi-AZ Deployment?
- Can I Change the VPC for a Created Instance?
- Can I Change the Region for a Created Instance?
- What Is Hidden Node?
- Database Versions
-
Resource and Disk Management
- Which Items Occupy the Storage Space of DDS Instances?
- Which Types of Logs and Files Occupy DDS DB Instance Storage Space?
- Why Is the Storage Space Usage Displayed on the GUI Smaller Than the Actual Usage?
- Why Does Available Disk Space Not Increase After Data Is Deleted?
- Why Is the Resident Memory of a 4 vCPUs/8 GB Memory Replica Set Instance Only 4 GB?
- Capacity Expansion and Specification Changes
-
Database Performance
- When Will a Primary/Standby Switchover Be Triggered for a Cluster or Replica Set?
- High Storage Usage
- What Is the Time Delay for Primary/Secondary Synchronization in a Replica Set?
- How Is Data Transferred Between the Primary and Secondary Nodes of a Replica Set?
- How Do I Clear an Alarm Saying the Shard Memory Usage Exceeds 90%?
- What Can I Do If a Query Error Is Reported After Data Is Written Into the DDS Cluster?
- Database Permissions
-
Creation and Deletion
- How Do I Select Instance Specifications and Nodes?
- Why Is an Instance Not Displayed on the Console After It Is Created?
- Can I Use a Template to Create DDS DB Instances?
- Why Is Data Missing from My Database?
- Will My Backups Be Deleted If I Delete My Cloud Account?
- What Are the Differences Between Instance Deletion and Unsubscription?
-
Database Connection
- What Should I Do If I Fail to Connect to a DDS Instance?
- What Can I Do If the Number of Connections of an Instance Reaches Its Maximum?
- How Do I Query and Limit the Number of Connections?
- What Should I Do If the ECS and DDS Are Deployed in Different VPCs and They Cannot Communicate with Each Other?
- Do Applications Need to Support Automatic Reconnecting to the DDS Database?
- How Do I Create and Log In to an ECS?
- Installing a Client
- Database Usage
- Database Migration
- Database Storage
- Database Parameters
- Backup and Restoration
- Network Security
- Monitoring and Alarm
- Change History (FAQs) Europe Site
-
Product Consulting
-
Troubleshooting
- DDS Instance Node Fault Handling Mechanism
- Connection Failure Message: network error while attempting to run command 'isMaster'
- Connection Failure Messages: No route to host and connection attempt failed
- Connection Failure Message: Authentication failed
- Connection Failure Message: couldn't connect to server
- Connection Failure Message: cannot list multiple servers in URL without 'replicaSet' option
- Connection Failure Message: Timeout while receiving message
- Connection Failure Message: exception: login failed and U_STRINGPREP_PROHIBITED_ERROR
- Change History (Troubleshooting) European Sites
- Videos
Read Replica
To improve the read capability of the primary node, DDS provides read replicas that can be accessed independently, which is good for handling read-intensive workloads and reducing memory pressure on the primary node. You can also create one or more read replicas to process a large number of read requests and improve throughput.
Differences Between Read Replica and Secondary Node
Node |
Description |
Application Scenario |
---|---|---|
Secondary nodes |
The secondary node of a replica set instance ensures high availability. If a primary node is faulty, the system automatically switches traffic to the secondary node. If the primary node is faulty, each secondary node may be elected as a new primary node to execute data write requests. |
DDS provides an HA connection address to connect to both the primary and secondary nodes and separate read and write operations. In this way, a DDS instance can handle heavy read workloads with ease. In addition, the impact of node faults on services is wakened while the performance is improved. |
Read replicas |
A read replica in a replica set instance synchronizes data only from the primary node. It does not ensure high availability and will not be elected as the primary node. Read replicas can be connected independently and do not interfere with primary nodes. |
Read replicas are useful when applications need to read large amounts of data from existing instances. |
Constraints
- Only replica set instances can have read replicas.
- Instances that only have read replicas cannot be created.
- DDS instance version must be 3.4, 4.0, and 4.2.
- Read replicas are used only for processing read requests and do not participate in primary/secondary node election.
- A maximum of five read replicas can be added to a replica set instance. For details, see Adding Read Replicas to a Replica Set Instance.
- Data is asynchronously replicated between the primary node and the read replica, and this process will delay by a few seconds.
Functions
- You can change the number of read replicas to meet fluctuating service demands and reduce service costs.
- The specifications of a read replica are the same as those of the primary node. Data is automatically synchronized to the read replica.
- Resources on the primary node are not occupied. Adding or deleting read replicas does not affect services on the primary node.
- Read replicas can be connected independently and do not interfere with existing primary and secondary nodes. For details, see Connecting to Read Replicas Using Mongo Shell.
- You can monitor the performance of read replicas.
Billing
- After a read replica is added to the current instance, you will be billed for using the VM and disks of the read replica.
- The price of a read replica is equal to that of a single node in a replica set instance or a shard node in a cluster instance. For example, if the price of a three-node replica set instance is USD $3,000, the price of a read replica is USD $1,000.
Feedback
Was this page helpful?
Provide feedbackThank you very much for your feedback. We will continue working to improve the documentation.