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Differences Between Azure SQL Database and SQL Server
In recent years, cloud computing has turned out to be one of the technological evolutions of the century. It has completely revolutionized the way businesses and consumers store and accesses their data. With the ability to instantly access servers, databases, networks, etc., we can accelerate both productivity and performance.
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However, it has not been surprising to witness Microsoft bidding to claim a sizeable market share in this lucrative market. In the last few years, Microsoft has been focusing more on cloud computing and storage and unveiled many products designed for the cloud. Among these, Azure SQL database and SQL server are some of the most notable ones.
The Azure SQL Database is a cloud-based service that is built to keep with SQL server. Thus, it is not surprising that it shares many similarities in functionality and compatibility with SQL server. That said, the two products are not the same; in fact, there are many fundamental differences between the two.
One of the most important decision points for businesses and users, in general, is whether to deploy Azure SQL Database or SQL Server on Azure VMs for their needs. Both database systems are optimized for different database needs and, therefore, it is unlikely to reach a sound decision without a detailed look into the differences between Azure SQL database and SQL server.
But before diving into the key differences, let’s explore what these two systems offer!
What is Azure SQL Database?
Azure SQL Database by Microsoft Azure Platform is a cloud-computing database service. It is used to host and use a relational SQL database in the cloud without the need for any hardware or software installation. The SQL database also comes with advanced features for users to make data management and handling a breeze.
Azure SQL Database is a fully managed cloud database (PaaS), which is provided as a part of Microsoft Azure. It is great for handling most of the database management functions, including upgrading, patching, backups, and monitoring. And the best part is that this is automatic and does not need user involvement. The SQL Database runs on the latest version of the SQL Server database engine and patched OS with 99.99% availability. The capabilities of this database allow you to focus on domain-specific database management and optimizing data, which is at the core of your business strategies.
Azure SQL Database can be the right choice for different cloud applications for the following reasons:
- High availability
- Automatic tuning, which is an autonomous artificial intelligence-based performance tuning option for fixing any performance-related problems without user involvement.
- Business continuity with remarkable backup and data restoring capabilities.
- Long-term backup retention allowing you to keep data backup for up to 10 years.
- With Geo-replication, you can virtually create readable secondary databases in different data center locations.
- The scaling database resources feature offers businesses and users the option to scale database resources both up or down.
Azure SQL Database offers two different purchasing models: a vCore-based purchasing model and a DTU-based purchasing model. These models help you easily define and scale performance using either of the two options. Microsoft also takes away the hassle out of the process of database management by patching and updating the SQL and operating system code itself. With that out of the way, even a beginner can easily manage the underlying infrastructure.
What is Microsoft SQL Server?
SQL Server by Microsoft is a relational database management system that comes with an assortment of add-on services. Since it is a database server, it is basically a software product with the main objective to store and retrieve data as requested by other software applications. Whether the request comes in from software that is on the same computer or on another computer across a network, SQL server works either way.
Microsoft offers a number of different editions of Microsoft SQL Server for different users as well as a range of different workloads. From small one-machine applications to large Internet-facing applications with multiple active users, there is an edition of SQL server available for all database needs. It is also one of the top three database technologies, including Oracle Database and IBM’s DB2.
Like many of its counterparts, Microsoft SQL Server is built on SQL. SQL is basically a standardized programming language that database administrators (DBAs) and other IT professionals use for database management and data evaluation that is held. The Server is also linked to Transact-SQL (T-SQL), which is an implementation of SQL from Microsoft. It offers an additional set of proprietary programming extensions to the standard SQL language.
The SQL Server Database Engine is at the center of the Microsoft SQL Server. It is designed to control data storage, processing, and security. It also has a relational engine that processes commands and queries. Plus, its storage engine maintains and organizes database files, tables, pages, indexes, data buffers and transactions. The creation and execution of stored procedures, triggers, views, and other database objects are also done by the Database Engine.
Right below the Database Engine, lies the SQL Server Operating System or SQLOS. This operating system is designed to carry out secondary functions like I/O management, job scheduling, memory, and securing data to eliminate any problems like conflicting updates. On top of the Database Engine is a network interface layer, which uses Microsoft’s Tabular Data Stream protocol. This is mainly to enable request and response interactions with database servers.
The SQL Server DBAs and developers, who are the users of SQL Server write T-SQL statements for various purposes. This includes building and modify database structures, putting security protections in place, manipulating data, and creating a backup of databases, etc.
Azure SQL Database Vs. SQL Server
Azure SQL database is based on SQL Server, which is mainly the reason that both share a lot of features. But despite some obvious similarities, both database systems are different in more ways than they are similar. As a matter of fact, contrary to the common misconception, the Azure SQL database is not the cloud version of SQL Server.
Before we get into discussing the more intricate differences between Azure SQL database and SQL Server, let’s get the fundamental difference out of the way. While in SQL server, databases are the only entity on the database server, whereas one database can host multiple databases from various customers on the Azure SQL database,. Simply put, the Azure SQL database has software multitenancy and allows all tenants to use its physical resources in real-time.
Now that you know the fundamental difference between the two, let’s head straight into other differences.
Azure SQL database is designed specially to allow SQL developers to use it easily for communication and authentication. This is also the primary reason why there isn’t much of a difference between the two when it comes to programming. Often the most you have to do is simply change the value of a parameter in the connection string and that gives you access to the Azure SQL database.
However, a notable difference can be observed in communication. When using the SQL Server, your application corresponds directly to the server over your LAN. Not just that, it also uses Tabular Data Stream (TDS) protocol over TCP/IP or HTTP. It can communicate on any configurable port without any need for transport security.
On the other hand, the Azure SQL database requires your application to make an explicit call, preferably through your network’s firewall. Moreover, this call from your application can only reach the Azure Gateway through the Internet. Therefore, the Azure SQL database uses only TCP/IP protocol for communication.
Once at the Gateway, there is another firewall called SQL Azure firewall. This firewall only lets through IP addresses that have been defined clearly to have access. After accessing the SQL Azure firewall, the call from your application finally makes the connection to the back-end data node with the help of Gateway as the proxy. All communications take place only through SSL and it goes only through port 1433.
Therefore, in comparison to SQL Server, Azure SQL database has a much more complicated structure. The primary reason for this complexity is to allow connections through the Internet and to serve multiple tenants.
Another important difference between Azure SQL database and SQL Server is that of database size. In the Azure SQL database, the database size always depends on the underlying service tier models. For instance, the Premium P15 service tier model would support up to 4 TB databases.
So, Azure SQL Database supports databases of up to 100 TB with the Hyperscale service tier model. Databases per logical server are 5000 DTU (Database Transaction Units) or eDTU (Elastic Database Transaction Units) while the quota is 54,000 per server.
In comparison to this, the database size for SQL Server depends on the size of the VM. SQL Server instances support up to 256 TB of storage. Thus, an instance can support as many databases as needed at a given time.
For example, a premium storage disk can deal with up to 32 TB of the database. The users also have the option to use Ultra disk, which comes in different sizes and can be customized for the range of input values.
Another important difference that gives Azure SQL database an edge over SQL Server is its high availability. The SQL database is essentially lauded for this advantage. By default, Azure SQL database’s infrastructure provides fault-tolerance and high availability for the databases. The SQL database and SQL Managed Instance also store data in Geo-redundant (RA-GRS) storage blobs by default. This can then be replicated to a paired region.
On the other hand, SQL Server infrastructure offers fault-tolerance and high availability for the VMs by default. You can easily use SQL level high-availability and disaster-recovery features. However, the benefits of high-availability come at a cost and additional overhead to manage your additional VM servers.
Data Definition Language
Data definition language or DDL is a syntax used for creating and modifying the structure of database objects. When it comes to DDL, there are a few features that the Azure SQL database does not support. This is mainly because of its architecture and the fact that it does not use an underlying hardware platform. Under this category, both the database systems differ in the following ways:
- Common language runtime: Unlike SQL Server, Azure SQL database does not support common language runtime (CLR). Consequently, SQL database system does not include views, stored procedures, triggers, and user-defined functions. This is because SQL database is multitenant and has to protect one user from accidentally or intentionally using others’ CLR objects on the same server.
- Extended stored procedures and table partitioning: Extended stored procedures in SQL Server are basically routines stored in DLLs. These procedures are written in C or C++ languages and use Open Data Services API to get parameters and deliver results. Similarly, table partitioning is another feature in SQL server that distributes table or index data across multiple file groups within the same database to boost performance. Azure SQL database doesn’t have either of these features.
- Clustered indexes: Clustered indexes allow the users to modify the order in which records are stored in a physical database. One table can essentially have just one clustered index. Having a clustered index is optional in SQL server, while all tables should have a clustered index in Azure SQL database. If all the tables do not have it, INSERT operations will automatically fail. This is again due to SQL database’s architecture and because it cannot support heap tables. If you ever have a need to transfer your data from SQL server to SQL database, you will first have to build clustered indexes for tables that lack them.
Database Mirroring and Fail-over Clustering
Azure SQL database is built on the Windows Azure platform that has to offer high availability. For this reason, it does not support database mirroring and fail-over clustering either. Each and every user database is copied twice on two different nodes. In case the primary node goes down, one of the two replicated copies will offer backup. Therefore, it is obvious that SQL database does not require an explicit fail-over clustering like SQL Server.
From all that we have discussed the Azure SQL database, we know that it is more logical than a physical entity. Therefore, the deployment architecture varies from SQL server to a great extent as well. The three entities found in the SQL cloud database system include subscription, server, and database. Subscription offers you the Windows Azure platform and the services that come as a part of it. This part of the database system determines the billing.
On the other hand, a server specifically means a logical grouping of databases that share a common data center. Hence, “database” is a logical representation of a database that exists as a partition within an SQL server database.
Database Backup and Restore
One of the greatest benefits of deploying the Azure SQL database is that it automatically backs up the database and transaction log periodically. This feature is a part of its business continuity strategy so that business operations can continue without interruption or delay. SQL database uses read-access Geo-redundant (RA-GRS) to provide Geo-redundancy. This means it offers a backup option to give your database cross-geographical durability so that you do not have to worry about data loss anymore.
Moreover, SQL database also allows you to restore the database at any point in time to give you backup for accidental deletions. In the case of regional outages, it allows you to restore the database from a different location.
This backup and restoration feature is by far the most important benefit of using Azure SQL database over SQL Server. While you can restore the database on SQL Server using SSMS and point-in-time restore according to the backup frequency and database recovery model, an automatic backup and restore is not a given in SQL Server.
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With the Azure SQL database, Microsoft has taken considerable steps to make the cloud database system appealing and fitting for both small and big businesses. In fact, it has been specifically designed in a way that the structure can be scaled to meet varying database needs.
That said, this does not make the Azure SQL database suitable for all applications and business needs. As a matter of fact, there are various features of SQL server that are not supported by this cloud version for its own good reasons. Therefore, depending on your needs for those features, SQL Server should be preferred over SQL database.