Common Concepts
Last updated: 2025-05-07 18:12:10
This document describes the common concepts of TencentDB for SQL Server to help you better understand and use it.
Database instance
A database instance is a database server. One or multiple databases can be created in a database instance, and one or multiple tables can be created in a 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 elastically expands the read capacity and mitigates the database pressures. In scenarios where there are many read requests but only few write requests, a single instance may not be able to handle the load of read requests, which even may affect the business. In this case, you can create one or multiple read-only instances and use them to sustain high numbers of database reads and increase the application throughput.
Tencent Cloud console
Tencent Cloud console consists of web-based UIs.
Region
The geographic location of a physical IDC. In general, a TencentDB for SQL Server instance and a CVM instance should be in the same region to achieve the best access performance.
Availability zone (AZ)
A physical location with independent power supply and network resources within a region. There are no substantial differences between different AZs in the same region.
Multi-AZ
A physical location created by combining multiple AZs in the same region.
RO group
A group of read-only instances.
Billing mode
The billing mode of an instance resource, pay-as-you-go billing mode and monthly subscription billing mode.
Pay-as-you-go
A postpaid billing mode, where you can apply for resources for on-demand use and will be charged based on the actual usage upon settlement.
Monthly Subscription
A prepaid billing mode, where users can fulfill their cloud resource requirements by making a one-time payment for a month, multiple months, or multiple years, based on their individual usage needs.
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 called a standalone instance. It has only one database node, separates computing and storage, and is very cost-effective.
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, the two-node instance with the version 2008R2 Enterprise, 2012 Enterprise, or 2016 Enterprise consists of SQL Server databases with the one-primary-one-mirror configuration. These are deployed across racks/AZs. Each database corresponds to a set of monitoring agents that monitor the database in real time through heartbeats.
The two-node instance with the version 2017 Enterprise or 2019 Enterprise uses the Always On architecture (including one primary node and one replica node). The primary/replica nodes are deployed across racks/AZs. Each database corresponds to a set of monitoring agents that monitor the database in real time through heartbeats.
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.
Supported versions are 2017 Enterprise, 2019 Enterprise, and 2022 Enterprise.
Engine versions
Compatible database versions. Currently, the following versions are supported: 2008 R2 Enterprise, 2012 Enterprise, 2016 Enterprise, 2017 Enterprise, and 2019 Enterprise.
Specification
Resource configuration of each node, such as 2-core 16 GB MEM.
Disk
The main storage device of a computer, i.e., data storage space.
Balanced SSD
It is based on Tencent Cloud's latest storage engine, NVMe SSD storage media and the latest network infrastructure. It employs a three-copy distributed mechanism to provide high-performance storage with low latency, high random IOPS, high throughput I/O, and data availability up to 99.9999999% (nine nines). It is applicable to business scenarios that have extremely high requirements for storage I/O performance and high-availability architecture at the application layer, such as online games, ecommerce, ERP software services, and video live streaming.
Enhanced SSD
It is an entry-level all-flash block storage product provided by Tencent Cloud. It's highly cost-effective and suitable for medium applications with high requirements for data reliability and standard requirements for performance, such as web/app servers, business logical processing, KV services, as well as basic database services.
High-performance local SSD
High-I/O local disk storage type.
SSD
It is an all-flash cloud disk storage type with NVMe SSD as the storage media. It adopts a three-copy distributed storage mechanism to provide low-latency and high-throughput I/O capabilities with a high random IOPS and 99.9999999% (nine nines) data security.
Premium cloud disk
It is a hybrid storage type. It provides high-performance storage capabilities close to SSD through the cache mechanism and adopts a three-copy distributed mechanism to ensure the data reliability.
Project
Used to categorize and manage instance resources.
Tag
A cloud resource management tool that allows you to use different standards to categorize, search for, and aggregate cloud resources with the same attributes.
Maintenance time
To ensure the stability of your TencentDB instance, the backend system performs maintenance operations on the instance during the maintenance window from time to time. We highly recommend that you set an acceptable maintenance time for your business instance, usually during off-peak hours, so as to minimize the potential impact on your business.
Security group
Security access control to instances by specifying IP, protocol, and port rules for instance access.
Network
A network made up of several nodes and linkages that connect them. It represents many objects and their interconnections. For performance and security considerations, only VPC network is supported currently.
Private network address
The IP and port assigned to a database for both read and write requests within your VPC network.
Port
A port in a computer, switch, or router.
Database
A set of organized, shared, and centrally managed data that is stored on a computer for a long period.
Database account
A username used to log in to and manage a database.
Character set
A mapping relationship or encoding rule, including a coded character set and character encoding. The code points corresponding to a character set are mapped into binary sequences, so that they can be stored and processed by a computer.
Cloud Virtual Machine (CVM)
A scalable computing service provided by Tencent Cloud.
SSMS
SQL Server Management Studio (SSMS) is an integrated environment to manage any SQL basic structures.
Alarm policy
You can create alarms to stay informed of the status changes of certain metrics. The specific metrics will be monitored for a certain period of time, and alarm notifications will be sent by SMS, email, and phone at specified intervals based on the given threshold.
Pub/Sub
Business data replication and sync. You can create, change, and delete pub/sub servers in the TencentDB for SQL Server console.
Recycle bin
A place where terminated instances are stored before elimination. Such instances can be restored.
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
You can set the backup time and cycle for the system to automatically and regularly save data.
Non-archive backup
Automatic backups include non-archive backups and archive backups with different backup retention policies. For non-archive backups, you can set the backup retention period and time by week, and you should back up your data at least twice a week.
Archive backup
Automatic backups include non-archive backups and archive backups with different backup retention policies. Archive backup is a more flexible backup policy on the basis of non-archive automatic backup. It supports setting the number of retained backups by month, quarter, or year and does not need to retain additional new backups. However, its retention period is different from (longer than) that of non-archive backup.
Manual backup
You can manually create backup files at any time.
Data backup
You can back up one, multiple, or all databases in an instance.
Log backup
The system automatically generates a log backup (log file) every 30 minutes and uploads it to the cloud for storage. You can download log files.
Backup policy
You can select instance backup or multi-database backup. The former backs up all databases in an instance, while the latter backs up selected databases.
Backup task configuration
It is used to set the global variables of manual and scheduled backups. You can set Upload Backup File (archive file or unarchived files) and select the primary or replica instance for backup.
Backup file format
It is used to set whether to upload an archive file or upload unarchived files for the instance.
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