This document introduces common concepts related to this product to help you better select and use SQL Server.
Database Instance
A database instance (Database Instance) is a database server (Database Server). You can create one or more databases (Database) within it, and you can create one or more tables within each database.
Primary instance and replica instance
For two-node (formerly HA Edition/Cluster Edition) instances and multi-node instances, the node that handles your business access is called the primary instance. Meanwhile, the data of the primary instance will be synchronized in real time to one or more other nodes (referred to as replica instances/nodes). Under normal circumstances, you can only access the primary instance, while the replica instance exists only as a backup and does not provide business access. When the read-only mode is enabled for the replica node, the replica node can provide read-only capabilities and can replace read-only instances. In the event of a primary instance failure, a primary/replica switch will occur. If the read-only mode is not enabled for the replica node, the entire switch process is transparent to the application, although there might be a brief disconnection during the switch. If the read-only mode is enabled for the replica node, the read-only feature for the replica node may experience a momentary disconnection or a prolonged interruption. You should ensure the business has a reconnection mechanism.
Read-only instance
A read-only instance is created to elastically scale read capacity and offload database pressure. In application scenarios where the database has few write requests but massive read requests, a single instance may be unable to handle the read load, potentially impacting the business. In such cases, you can create one or more read-only instances to meet the massive database read demands and increase application throughput.
Tencent Cloud Console
A web-based user interface.
Region
A region refers to the geographical area of a physical data center. Generally, a SQL Server instance should reside in the same region as the CVM instance to achieve optimal access performance.
Availability zone
An AZ is a physical zone within a region that has independent power and network. Different AZs within the same region are generally consistent in terms of product features. However, the specific resource availability and capabilities are subject to what is displayed on the console.
Multi-AZ
A Multi-AZ is a physical zone formed by combining multiple single AZs within the same region.
RO group
An RO group is a collection composed of multiple read-only instances. It is the RO group for read-only instances.
Billing mode
The billing method for instance resources is divided into yearly/monthly subscription and pay-as-you-go.
Pay-as-you-go
This is a postpaid billing method. You first apply for resources on demand, and fees are charged based on your actual resource usage during settlement.
Yearly/Monthly Subscription
With prepaid billing, users pay a one-time fee for one month, multiple months, or multiple years based on their cloud resource usage requirements.
Instance type
By deployment architecture, instances are divided into single-node (formerly Basic Edition), two-node (formerly HA Edition/Cluster Edition), and multi-node.
Single-node (formerly Basic Edition)
A TencentDB for SQL Server single-node (formerly Basic Edition) instance is also referred to as a standalone instance. It has only a single database node, features compute-storage separation, and offers a relatively low usage cost.
Two-node (formerly HA Edition/Cluster Edition)
A two-node instance consisting of a one-primary-one-replica architecture. When the primary instance fails and becomes inaccessible, it will automatically switch to the replica instance.
Among them, two-node instances of the 2012 Enterprise, 2014 Enterprise, and 2016 Enterprise editions consist of a one-primary-one-mirror SQL Server database. They are deployed across racks/AZs. Each database corresponds to a set of monitoring agents, which perform real-time monitoring of the database via heartbeat.
Two-node instances of the 2017 Enterprise, 2019 Enterprise, 2022 Enterprise, and 2025 Enterprise editions adopt the Always On architecture (including one-primary-one-secondary). The primary and secondary nodes are deployed across racks/AZs. Each database corresponds to a set of monitoring agents, which perform real-time monitoring of the database via heartbeat.
Multi-node
A multi-node instance consisting of a one-primary-multiple-replica architecture. It can be deployed as a three-node, four-node, five-node, or six-node architecture. When the primary instance fails and becomes inaccessible, it will automatically switch to the replica instance.
It supports the 2017 Enterprise, 2019 Enterprise, 2022 Enterprise, and 2025 Enterprise editions.
Engine Version
Compatible database editions currently supported: 2012 Enterprise, 2014 Enterprise, 2016 Enterprise, 2017 Enterprise, 2019 Enterprise, 2022 Enterprise, and 2025 Enterprise.
Specification
The resource configuration for each node, for example, 2 cores and 16 GB.
Hard Disk
It is the primary storage device of a computer, providing space for storing data.
General Purpose SSD CBS
Tencent Cloud offers a product type designed with a next-generation storage engine, built on all-NVMe SSD storage media and network infrastructure. It employs a three-replica distributed mechanism to deliver I/O capabilities with low latency, high random IOPS, and high throughput, as well as storage services with data durability of up to 99.9999999%. This product is suitable for business scenarios that have extremely high requirements for storage I/O performance and also possess a highly available application-layer architecture, such as online gaming, e-commerce, ERP software service providers, and live video streaming.
Enhanced SSD CBS
Enhanced SSD CBS is an entry-level all-flash block storage product launched by Tencent Cloud. It offers high cost-effectiveness and is suitable for medium-sized application scenarios that require high data reliability and moderate performance, such as Web/App servers and business logic processing.
High-Performance Local SSD
High I/O local disk storage type.
Cloud SSD
Based on the all-flash storage type provided by NVMe SSD storage media and employing a three-replica distributed mechanism, it delivers I/O capabilities with low latency, high random IOPS, and high throughput, as well as storage services with data durability of up to 99.9999999%.
High-Performance Cloud Disk
Hybrid storage type delivers high-performance storage capabilities close to those of solid-state storage through a Cache mechanism, while ensuring data reliability by employing a three-replica distributed mechanism.
Project
It is used for classifying and managing instance resources.
Tag
Tag is a cloud resource management tool provided by Tencent Cloud. You can use it to classify, search, and aggregate cloud resources with similar characteristics from different dimensions, thereby easily managing your cloud resources.
Maintenance Window
To ensure the stability of cloud database instances, the backend system performs maintenance operations on instances irregularly within a time window. You can configure an acceptable maintenance time for your business instances, typically during off-peak hours, to minimize the impact on your business.
Security Group
It performs secure access control on instances by specifying the IP addresses, protocols, and port rules for traffic entering the instances.
Network
A network consists of multiple nodes and the links connecting these nodes, representing various objects and their interconnections. For performance and security considerations, only VPC is currently supported.
Private Network Address
It is the IP address and port assigned to the database within the user's VPC network, supporting both read and write requests.
Port
Port refers to a port inside a computer or within a switch/router.
Database
A database is a collection of a large amount of data that is persistently stored in computers, organized, shareable, and centrally managed.
Database Account
It is the username used to log in to and manage the database.
Character Set
It includes a character encoding set and character encoding. In simple terms, it is a mapping relationship or an encoding rule. The code points corresponding to the character set are mapped to binary sequences, enabling computers to store and process the data.
CVM
Cloud Virtual Machine (CVM) is a scalable computing service provided by Tencent Cloud.
SSMS
SQL Server Management Studio (SSMS) is an integrated environment for managing any SQL infrastructure.
Alarm Policy
When certain monitoring metrics become abnormal, an alarm is created to promptly notify you to take action. Within a specified period, specific metrics are monitored based on given thresholds. Alarm notifications are then sent via multiple channels (SMS, email, phone) at regular intervals.
Publish/Subscription
It refers to the replication and synchronization of business data. You can self-service create, modify, and delete publishing and subscription servers on the TencentDB for SQL Server console.
Recycle Bin
The Recycle Bin is the location where terminated instances are stored before they are decommissioned. You can restore terminated instances from the Recycle Bin. The specific retention period, recoverable scope, and restoration rules are subject to the product documentation and console display.
Backup
To cope with potential accidental situations such as file/data loss or damage, the data is stored separately or saved in the form of file replicas.
Local backup
The backup within the same region as the instance.
Cross-region backup
The backup in a different region from the instance, that is, a solution that stores the local backup files in another region for saving.
Automatic Backup
It is a method for the system to autonomously and periodically save data, which is achieved by configuring the backup time and cycle.
Regular Backup
Depending on the backup retention policy, automatic backups are categorized into two scenarios: regular backup and periodic backup. Regular backup allows you to configure the backup retention period and time on a weekly basis, with a minimum requirement of two backups per week.
Periodic Backup
Depending on the backup retention policy, automatic backups are categorized into two scenarios: regular backup and periodic backup. Based on regular automatic backup, periodic backup offers a more flexible backup policy (allowing you to set the number of backups to retain on a monthly, quarterly, or yearly basis). It does not require retaining additional new backup files, but the backup retention duration for periodic backup differs from (and is longer than) that of regular backup.
Manual Backup
It supports creating backup files manually at any time.
Data Backup
It refers to backing up a single database, multiple databases, or all databases within an instance.
Log Backup
The system automatically generates log backups (log files), performs log backups every 30 minutes, uploads them to cloud storage, and supports downloading log files.
Backup Policy
You can choose to back up as instance backup or multi-database backup. With instance backup, you can back up all databases within an entire instance. With multi-database backup, you can select the specific databases that need to be backed up.
Configure Backup Task
It is used to configure global variables for manual backup and scheduled backup, supporting the selection and configuration of backup file format (single-database backup or archived backup) and master or slave instance backup.
Backup File Format
It is used to configure whether the instance's backup files are archived backup files or single-database backup files.