Database Engine Instances (SQL Server)
An instance of the Database Engine is a copy of the sqlservr.exe executable that runs as an operating system service. Each instance manages several system databases and one or more user databases. Each computer can run multiple instances of the Database Engine. Applications connect to the instance in order to perform work in a database managed by the instance.
Instances
An instance of the Database Engine operates as a service that handles all application requests to work with the data in any of the databases managed by that instance. It is the target of the connection requests (logins) from applications. The connection runs through a network connection if the application and instance are on separate computers. If the application and instance are on the same computer, the SQL Server connection can run as either a network connection or an in-memory connection. When a connection has been completed, an application sends Transact-SQL statements across the connection to the instance. The instance resolves the Transact-SQL statements into operations against the data and objects in the databases, and if the required permissions have been granted to the login credentials, performs the work. Any data retrieved is returned to the application, along with any messages such as errors.
You can run multiple instances of the Database Engine on a computer. One instance can be the default instance. The default instance has no name. If a connection request specifies only the name of the computer, the connection is made to the default instance. A named instance is one where you specify an instance name when installing the instance. A connection request must specify both the computer name and instance name in order to connect to the instance. There is no requirement to install a default instance; all of the instances running on a computer can be named instances.
Related Tasks
| Task Description | Topic |
|---|---|
| Describes how to configure the properties of an instance. Configure defaults such as file locations and date formats, or how the instance uses operating system resources, such as memory or threads. | Configure Database Engine Instances (SQL Server) |
| Describes how to manage the collation for an instance of the Database Engine. Collations define the bit patterns used to represent characters, and associated behaviors such as sorting, and case or accent sensitivity in comparison operations. | Collation and Unicode Support |
| Describes how to configure linked server definitions, which allow Transact-SQL statements run in an instance to work with data stored in separate OLE DB data sources. | Linked Servers (Database Engine) |
| Describes how to create a logon trigger, which specifies actions to be taken after a logon attempt has been validated, but before it starts working with resources in the instance. Logon triggers support actions such as logging connection activity, or restricting logins based on logic in addition to the credential authentication performed by Windows and SQL Server. | Logon Triggers |
| Describes how to manage the service associated with an instance of the Database Engine. This includes actions such as starting and stopping the service, or configuring startup options. | Manage the Database Engine Services |
| Describes how to perform server network configuration tasks such as enabling protocols, modifying the port or pipe used by a protocol, configuring encryption, configuring the SQL Server Browser service, exposing or hiding the SQL Server Database Engine on the network, and registering the Server Principal Name. | Server Network Configuration |
| Describes how to perform client network configuration tasks such as configuring client protocols and creating or deleting a Server Alias. | Client Network Configuration |
| Describes the SQL Server Management Studio editors that can be used to design, debug, and run scripts such as Transact-SQL scripts. Also describes how to code Windows PowerShell scripts to work with SQL Server components. | Database Engine Scripting |
| Describes how to use maintenance plans to specify a workflow of common administration tasks for an instance. Workflows include tasks such as backing up databases and updating statistics to improve performance. | Maintenance Plans |
| Describes how to use the resource governor to manage resource consumption and workloads by specifying limits to the amount of CPU and memory that application requests can use. | Resource Governor |
| Describes how database applications can use database mail to send e-mail messages from the Database Engine. | Database Mail |
| Describes how to use extended events to capture performance data can be used to build performance baselines or to diagnose performance problems. Extended events are a light-weight, highly scalable system for gathering performance data. | Extended Events |
| Describes how to use SQL Trace to build a customized system for capturing and recording events in the Database Engine. | SQL Trace |
| Describes how to use SQL Server Profiler to capture traces of application requests coming in to an instance of the Database Engine. These traces can later be replayed for activities such as performance testing or problem diagnosis. | SQL Server Profiler |
| Describes the Change Data Capture (CDC) and Change Tracking features and describes how to use these features to track changes to data in a database. | Track Data Changes (SQL Server) |
| Describes how to use the Log File viewer to find and view SQL Server errors and messages in various logs, such as the SQL Server job history, the SQL Server logs, and Windows event logs. | Log File Viewer |
| Describes how to use the Database Engine Tuning Advisor to analyze databases and make recommendations for addressing potential performance problems. | Database Engine Tuning Advisor |
| Describes how the production database administrators can make a diagnostic connection to instances when standard connections are not being accepted. | Diagnostic Connection for Database Administrators |
| Describes how to use the deprecated remote servers feature to enable access from one instance of the Database Engine to another. The preferred mechanism for this functionality is a linked server. | Remote Servers |
| Describes the capabilities of Service Broker for messaging and queueing applications and provides pointers to the Service Broker documentation. | Service Broker |
| Describes how the buffer pool extension can be used to provide seamless integration of nonvolatile random access storage (solid-state drives) to the Database Engine buffer pool to significantly improve I/O throughput. | Buffer Pool Extension File |
What is a SQL Server instance?
When I install SQL Server 2008 Express in prompts me to create an instance and aborts if I don’t. Then I see that information in an entry in Sql Server Configuration Manager on SQL Server Services. What is a SQL Server instance?
asked May 24, 2009 at 9:59
Pablo Fernandez Pablo Fernandez
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2 Answers 2
An SQL Server instance is a complete SQL server and you can install many instances on a machine but you can have only 1 default instance.
An SQL Server instance has its own copy of the server files, databases and security credentials.
This url may help you
answered May 24, 2009 at 10:42
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Can more than one instance be running at the same time?
May 24, 2009 at 10:53
Yes, more than 1 instance can run at a time. You just need a unique name for each instance that you install (as well as filesystem path)
May 24, 2009 at 10:57
You can even have one instance be SQL 2000 and another 2005; biggest gotcha with multiple instances is memory management, if you use the default settings, all instances will try to claim all memory, it’s best to explicitly limit max memory at each instance.
May 24, 2009 at 11:20
SQL 2000 supports 16 instances. SQL 2005 and SQL 2008 support up to 50 instances per computer. You can run SQL 2000 and SQL 2005 on the same computer, or SQL 2005 and SQL 2008 on the same computer. However you can not run SQL 2000 and SQL 2008 on the same computer.
May 25, 2009 at 3:16
Be aware that not all SQL Server services are «instance aware» or multi instance. Integration Services, for example, is only installed once per Windows host. These instances include Express instances that might be installed by applications.
May 29, 2009 at 20:05
SQL SERVER INSTANCE An instance of the Database Engine is a copy of the sqlservr.exe executable that runs as an operating system service. Each instance manages several system databases and one or more user databases. Each computer can run multiple instances of the Database Engine independently of other instances.
SQL Server is composed of three main parts: 1. An engine, which is the software started by a few Windows services that performs lookups, sorts, and other actions; 2. Meta-data such as the master and msdb system databases; 3. User databases where data is stored.
The master database contains the information that the engine reads when it starts up. It includes such things as security settings, file locations, sort orders, and database locations. The msdb database contains the information used by the SQL Server Agent program and information about maintenance plans. Yet another system database, called model, is the "template" from which other databases are created. Finally, the tempdb database is the "scratch" area that the engine software uses. This format holds true for all versions of SQL Server, although other control mechanisms are also implemented as Dynamic Link Libraries, or DLL’s. This means that a single installation of SQL Server has only one set of certain data, such as server-level security credentials, scheduling information, temporary files and other meta-data. Beginning with SQL Server 2000, you can run multiple copies of the software, using what Microsoft calls Instances. Instances share a few files between them, mostly dealing with client tools. This allows you to have two different system administrators (sa accounts) and other server-level security on the same hardware. So if you have different security needs, say running more than one company with different administrators, you can install multiple copies of SQL Server on the same hardware. Another advantage is that since some of the files that run the Instance are duplicated, you can apply service packs separately to each Instance. That way you can host several applications on the same hardware that require different service pack levels. Instances also allow you to work with multiple versions and even editions of the product. You can install Instances at any time, even after SQL Server is installed and running for some time. So for Instance (no pun intended), you can install SQL Server 2005 Express Edition, SQL Server 2005 Enterprise Edition, SQL Server 2008 Standard Edition and SQL Server 2008 R2 Developer Edition, all on the same hardware.
If a connection request specifies only the name of the computer only, then connection is made to the default instance. A named instance is one where you specify an instance name when installing the instance. A connection request must specify both the computer name and instance name in order to connect to the instance. The computer name and instance name are specified in the format computer_name\instance_name. Instances apply primarily to the database engine and its supporting components, not to the client tools. When you install multiple instances, each instance gets a unique set of: 1. System and user databases. 2. The SQL Server and SQL Server Agent services. For default instances, the names of the services remain MSSQLServer and SQLServerAgent. For named instances, the names of the services are changed to MSSQL$instancename and SQLAgent$instancename, allowing them to be started and stopped independently of the other instances on the server. The database engines for the different instances are started and stopped using the associated SQL Server service. The SQL Server Agent services manage scheduled events for the associated instances of the database engine. 3. The registry keys associated with the database engine and the SQL Server and SQL Server Agent services separate versions and releases.. 4. Network connection addresses so that applications can connect to specific instances.
What is mean by ‘server’,’instance’ in MSSQLServer 2005
A server is a (physical or virtual) machine hosting SQL Server software.
An instance is a collection of SQL Server databases run by a single SQL Server service, ahem, instance. You can view each separate instance you’re running in your service console. Each instance can be started or stopped individually.
You’re meant to use instances to partition data and policies. Each instance has completely separate databases, connection configuration, and security credentials.
answered Oct 5, 2010 at 7:50
Michael Petrotta Michael Petrotta
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If there are multiple server installations on single machine they are identified by instance name. In your connection string use format \ for non-default instances.
answered Oct 5, 2010 at 7:48
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An instance is an Environment which is used to Create a Multiple Database and connect to the Application server through an interface to retrieve the data from Backend to the Application for Enduser.
answered Sep 23, 2013 at 13:20
Rakesh Reddy Rakesh Reddy
I’ve seen a nice explanation from Reddit by Brandon Leach that
Since SQL Server is software like any other, you can have multiple installations. Both installations can be running on the same box at the same time. Say I have a server called “ Server1 ″ and two instances called “ Instance1 ” and “ Instance2 ″. In order to access Instance1 in my connection string I would use “ Server1\Instance2 ” as my server name. Instance1 in our scenario was installed first so it is the default instance, meaning I can just use “ Server1 ” as my server name.
answered Nov 15, 2020 at 11:05
Soner from The Ottoman Empire Soner from The Ottoman Empire
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What is «an instance» of a server?
The body of design for (a) coded function(s) is called a «CLASS».
To use the designed elements, coding, and functionality of a class, you need to build (define) a housing for it called an «OBJECT».
Thus the «OBJECT» is an «instance» (real thing) of a «Class» (only a design, no substance).
It’s like a blueprint is a plan to build a house, say. and when you build the house, it is an instance of the plan. Thus the plan is the class, and the house is the object.
Bottom Line: A Server (class) must be «instantiated» to create an actual working Server «object» which is a set of working functions to manage and deal with stored data. (see Tables, elsewhere)
What is a SQL Server Instance
In this article let us learn what is SQL Server Instance is. SQL Server allows us to install and run multiple instances of SQL Server or install SQL Server on a computer, where another version of SQL Server is already installed. You can refer to the article on How to download and install SQL Server.
Table of Contents
- What is SQL Server Instance
- Instance Name
- Instance Configuration
- Naming the instance
- Summary
What is SQL Server Instance
The SQL Server allows us to install multiple instances of the SQL Server database engines. These engines run side by side and completely isolated from each other. Each database engine installation is known as the SQL Server instance.
Every instance is a complete SQL Server Installation along with its own copy of server files, database engine, databases, Users and credentials.
The instances can be of the same SQL server version or of different versions.
Running multiple instances will use considerably more resources since you are running multiple SQL Servers on the same box.
Instance Name
We give a unique name to each instance so as to uniquely identify them.
We connect to the SQL Server using the \ as server name
For Example, if the computer name is HOME and the instance name is SQL2017 then SQL server name is HOME\SQL2017
We assign the instance name when we install the SQL Server database engine.
Instance Configuration
The SQL Server Instance configuration window asks for us to choose between two options. One is the default instance and the other one is named instance.
The default instance name is MSSQLSERVER. You do not have to specify the instance name when you want to connect to the default instance. You can have only one default instance installed on the PC. This is regardless of the SQL Server version
A Unique name must be given to a named instance. You can install SQL Server as a named instance without installing the default instance first.
You can create multiple instances by running the setup again. Refer to the article on How to download and install SQL Server
Naming the instance
The following rules must be followed when you name an instance of SQL Server:
- Instance names are not case sensitive.
- Names cannot start or end with an underscore ().
- Reserved Keywords are not allowed in the instance name. Here is the list of Reserved Keywords
- If you specify MSSQLSERVER as the instance name, the default instance will be created
- Name cannot be more than 16 characters
- The first character of the instance name must be a letter. a-z, A-Z Subsequent characters can be decimal numbers, the dollar sign ($), or an underscore ().
- Do not use the Spaces, backslash (), comma (,), colon (:), semi-colon (;), single quote (‘), ampersand (&), hyphen (-), and (@), etc
Summary
In this article, we learned what is SQL Server Instance is. In the next tutorial, we will learn how to connect to an Instance using the SSMS