Installing the default instance
Another approach is to remove the instance name during setup. In this case, SQL Server Express is installed as the default instance, assuming there isn't already a default instance installed. Only one server instance can be installed in this way. Again, if this is the only instance installed on your system there is very little difference between the other configurations, except when it comes time to connect to SQL Server Express, as I discuss later.

Choosing the System Administrator's Password
The SA password is the key that unlocks the entire database. The system administrator is permitted to do anything with or to the databases or the information they contain. The SA can add, change, or remove databases—all without anyone knowing the changes have been made. It's critical that this password be set correctly and protected.

When you install SQL Server Express using a common instance, there is only one SA password to worry about. Since the SA account is only accessible when you choose to install using Windows Authentication, the SA password need never be revealed. In any case, when you install SQL Server Express you're asked to provide an SA password, but this could be set to a random (hidden) value in the released versions.

Microsoft recommends that you configure your SQL Server Express instance to use Windows Integrated Security Authentication. This means the computer and Windows domain system administrator accounts are granted full SA access to the SQL Server Express instance. Sure, you'll need to be a computer or domain administrator to perform maintenance, install databases, and perform operations as simple as changing the database table values. This does not mean everyone who uses SQL Server Express should be an administrator. It does mean that, as part of the setup regimen, you'll need to create a "user" or application Login and set appropriate permissions on the tables, views, functions, and stored procedures that your application needs. I discuss this in more detail later.

Performance
SQL Server Express has abandoned the concept of a "governor". Frankly, I've rarely seen the governor slow any MSDE system down, but by dropping the governor, Microsoft has removed a point of confusion about the scalability of the SQL Server engine. SQL Server Express has ways to limit scalability. As configured in the Beta, SQL Server Express can only address 1GB of system RAM in the buffer pool. This limits the number of data pages and procedures in the RAM cache. Any SQL Server pro can tell you that the easiest way to improve performance is to add memory to the cache. Limiting visible RAM to 1GB means that you'll (eventually) run out of performance as you add load to the SQL Server Express instance. Does that mean SQL Server Express can support 1000 users? Sure, if the load placed on the SQL Server Express instance is not that great. In the same way, 10 users could bog down SQL Server Express, especially if the application is not written very efficiently.

SQL Server Express is also limited to a single processor instead of being able to run threads on additional processors (up to two) if your system supports it. This limitation also tends to scale back the upper limit of the performance you can expect from SQL Server Express.

When an application using SQL Server Express ends, SQL Server does not shut down. There is no auto-shutdown option in the SQL Server Express version. Because of this, the SQL Server engine is left in memory and continues to consume system RAM and CPU resources even after your application has ended. It's possible to write SQL Management Objects (SMO) routines to shut down the SQL Server Express instance, but this needs to be done only when you're sure it's not being shared by other applications.

Scalability
While MSDE databases were limited to 2GB, SQL Server Express database files are "limited" to 4GB. This means you can store twice as much data as before. Frankly, this puzzles me. I've worked with large corporate databases on a mainframe that fit nicely on a single 40MB disk pack. I guess people like to use the database to store a lot of documents and pictures of their pets. As with MSDE, the log file size is not limited—at least artificially. You still need to back up and truncate the logs periodically as I discuss later.

Tools
Microsoft has changed its approach to the tools as well. Even if you don't count the new GUI setup, when you download the SQL Server Express Beta 2, a new version of OSQL, SQL Computer Manager (MMC snap-in) and SQLCMD command-line tools are included to help manage the SQL Server Express instance. In addition, Microsoft plans to have a new GUI tool (tentatively named SQL Express Manager) to perform the initial configuration and periodic maintenance of SQL Server databases. This tool, which will soon be available as a separate download, is basically a tool not unlike SQL Query Analyzer to do user account setup and maintenance and help write, test, and debug SQL queries. You won't be able to connect to SQL Server Express with any other tools, including Management Studio or SQL Enterprise Manager. However, I expect that by the time it ships, SQL Server Express will be accessible from any of the current tools.

Administration
All of the tasks you had to do to administer MSDE have to be done with SQL Server Express, just as they have to be done with other versions of SQL Server. I would love to see an automated log backup script that periodically dumps the database and logs, and then truncates the log. Perhaps that's something that an enterprising third party needs to create. Until then, I recommend developers build these admin tasks into their applications and use SMO to perform these needed maintenance functions and use Windows Scheduler to help.

Service Packs
SQL Server Express can only be installed using the Windows Installer (MSI) installation package files. Unlike MSDE, you won't be able to create custom MSM setup scripts. In other respects it's the same as MSDE, so you'll still need to be prepared to update the SQL Server engine via the traditional Service Pack means. The folks at Microsoft are acutely aware of the issues in this regard and are still formulating a better strategy.




source : http://msdn2.microsoft.com/en-us/sqlserver/aa336270.aspx

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