1. SQLOS: which implements the basic services required by MS SQL Server, including thread scheduling, I/O stat management and memory management.

2. Relational Engine: which implements the relational database components including support for databases, tables, queries and stored procedures as well as implementing the type system.

3. Protocol Layer: which exposes the MS SQL Server functionality.

SQLOS

SQLOS is the base component in the Windows SQL Server architecture. It implements functions normally associated with the Operating System, thread scheduling, memory management, I/O management, buffer pool management, resource management, synchronization primitives and locking, and deadlock detection. Because the requirements of Windows SQL Server are highly specialized, it implements its own memory and thread management system, rather than using the generic one implemented in the OS. SQLOS also includes synchronization primitives for locking as well as monitoring for the worker threads to detect and recover from deadlocks.

SQLOS handles the memory requirements of MS SQL Server as well. Reducing disc I/O is one of the primary goals of specialized memory management in SQL Server. It maintains a buffer pool, which is used to cache data pages from the disc, and to satisfy the memory requirements for the query processor, and for other internal data structures. SQLOS monitors all the memory allocated from the buffer pool, ensuring that the components return unused memory to the pool, and shuffles data out of the cache to make room for newer data. For changes that are made to the data in buffer, SQLOS writes the data back to the disc lazily, that is when the disc subsystem is either free, or there have been significant numbers of changes made to the cache, while still serving requests from the cache. For this, it implements a Lazy Writer, which handles the task of writing the data back to persistent storage.

WIndows SQL Server normally supports up to 2 GB memory on x86 hardware, though it can be configured to use up to 64 GB if the Address Windowing Extension is used in the supporting operating system. For x64 hardware, it supports 8 TB of memory, and 7 TB for IA-64 systems (currently it is limited by Windows Server 2003 SP1 to 1TB). However, when running x86 versions of SQL Server on x64 hardware, it can access 4 GB of memory without any special configuration.

Relational Engine:

The Relational engine implements the relational data store using the capabilities provided by SQLOS, which is exposed to this layer via the private SQLOS API. It implements the type system, to define the types of the data that can be stored in the tables, as well as the different types of data items (such as tables, indexes, logs etc) that can be stored. It includes the Storage Engine, which handles the way data is stored on persistent storage devices and provides methods for fast access to the data. The storage engine implements log-based transaction to ensure that any changes to the data are ACID compliant. It also includes the query processor, which is the component that retrieves data. MSSQL queries specify what data to retrieve, and the query processor optimizes and translates the query into the sequence of operations needed to retrieve the data. The operations are then performed by worker threads, which are scheduled for execution by SQLOS.

Protocol Layer:

Protocol layer implements the external interface to MS SQL Server. All operations that can be invoked on MSSQL Server are communicated to it via a Microsoft-defined format, called Tabular Data Stream (TDS). TDS is an application layer protocol, used to transfer data between a database server and a client. Initially designed and developed by Sybase Inc. for their Sybase MS SQL Server relational database engine in 1984, and later by Microsoft in Microsoft MS SQL Server, TDS packets can be encased in other physical transport dependent protocols, including TCP/IP, Named pipes, and Shared memory. Consequently, access to MSSQL Server is available over these protocols. In addition, the MSSQL Server API is also exposed over web services.

MS SQL 2005 Server was released after 5 servers of it previous SQL version, MS SQL 2000, Hence it required allot to revisions to cope up with the current windows development environment. Therefore MS SQL 2005 SP2 had major changes in it, with too many performances and security fixes. Microsoft could not add few revisions due to its basic development structure however they had all the scope to introduce them in SQL 2008 release. And indeed, MS SQL 2008 has many installation as well as performance fixes being applied to it and allowing Windows Administrators to have full control on SQL activities. The biggest advantage of SQL 2008 over SQL 2005 is the ability to manage and maintain server performance. SQL 2008 does not require too much resource which is the best deal for today’s Shared Hosting environment. Also an upper hand to whose to do not want to invest too much on hardware of their dedicated servers just to run SQL server on it.

I have tried to gather the major improvement introduced by Microsoft on SQL 2008 from Internet which is an advantage over SQL 2005 however it all depends on what features are useful to you in the development of your ASP .NET applications. But switching to Microsoft SQL 2008 is definitely going to improve the performance even if you don’t use any of the below feature. And not to forget that with the release of SQL 2008, Microsoft will announce “End Of Life” for SQL 2000 version, which will mean that there won’t be any official support or update release for SQL 2000.

Major difference between SQL 2005 and SQL 2008.

* Easy Upgrades: Version upgrades are now very easy and effective with SQL 2008.
* Resource Restriction Governor: We set a restriction on a users or groups from consuming high resources. This is a very good feature that can be used on Windows shared server with SQL database to maintain the performance.
* Dates and Times settings: New data types such as: Date, Time, Date Time Offset has been introduced.
* Improved Full Text Search: Ability to backup Native Indexes and also thesaurus them as metadata.
* External Key Management: This unique can store Keys separately and not with the data.
* Improved SQL Server Analysis Service: It now has improved Stacks and computes block faster.
* Improved Installation: Microsoft has added an option where you can uninstall Disk images and service packs.
* Data Synchronizing: A Development of databases used in applications that frequently get disconnected.
* Transparent Data Encrypts: It has the ability to encrypt full SQL database with different encryption Methods.

* SQL Server Integration Service: SQL 2008 Server has improved multiprocessor support and faster lookups in compare to SQL 2005.
* Change Data Capture: Allows all changes to be captured and queried. (Enterprise). Also allows us to get detailed information on what changes has happened to which rows after a specific version.
* LINQ: A Development query language for accessing multiple type of data like XML and SQL at the same time.
* Hot Plug CPU: With this feature to an add CPUs on fly for your SQL server to use.
* Microsoft Office 2007 integration: One can use MS OFFICE as an SSRS template, like SSRS to WORD.
* Spatial Data types: Data types for storing Longitude, Latitude and GPS entry of a particular database.
* MERGE: A new TSQL command as a combination Update, Insert and Delete.
* Encrypted Backups: We can execute it at the time running backups to prevent tampering from external resource.
* Data Compression: This feature is different as it allows us to manage data compression at table level to enhance performance.
* Dynamic Development: Latest Visual Studio and ADO options along with ASP .Net 3.
* Reporting Server Performance: Unlike in SQL 2005 we can set threshold on Reporting server for memory management.
* Performance Studio: It is a Gallery that has collection of monitoring tools enhanced performance.
* Audits: A very power feature for monitoring the data access of your SQL database.
* Table Value Parameters: SQL 2008 database has ability to insert entire table into a stored procedure.
* Entity Database Services: (LOB) Line Of Business framework and (eSQL) Entity Query Language.

No doubt that Microsoft has improved all the features that has been used by hosting services. Even SQL Cluster in version 2008 has few major advantages since every one in today world wants to have their site up all the time with 100% uptime. I hope I get some time to write on “MS SQL 2008 Clustering..“