TAILIEUCHUNG - Microsoft SQL Server 2008 R2 Unleashed- P147

Microsoft SQL Server 2008 R2 Unleashed- P147:SQL Server 2005 provided a number of significant new features and enhancements over what was available in SQL Server 2000. This is not too surprising considering there was a five-year gap between these major SQL Server 2008 is not as much of a quantum leap forward from SQL Server 2005 | 1404 CHAPTER 38 Database Design and Performance nature and are not affected by the version of the database management system. This chapter focuses on those relatively unchanged principles. There are however some new features in SQL Server 2008 that will augment these basic principles. Filtered indexes new query and table hints plus other table-oriented features are just a few things you should consider when designing your database for performance. These features are discussed in detail in Chapter 24 Creating and Managing Tables Chapter 34 Data Structures Indexes and Performance and other chapters in Part V SQL Server Performance and Optimization. Basic Tenets of Designing for Performance Designing for performance requires making trade-offs. For example to get the best write performance out of a database you must sacrifice read performance. Before you tackle database design issues for an application it is critical to understand your goals. Do you want faster read performance Faster write performance A more understandable design Following are some basic truths about physical database design for SQL Server 2008 and the performance implications of each It s important to keep table row sizes as small as possible. Doing so is not about saving disk space. Having smaller rows means more rows fit on a single 8KB page which means fewer physical disk reads are required to read a given number of rows. You should use indexes to speed up read access. However the more indexes a table has the longer it takes to insert update and delete rows from the table. Using triggers to perform any kind of work during an insert an update or a delete exacts a performance toll and decreases concurrency by lengthening transaction duration. Implementing declarative referential integrity via primary and foreign keys helps maintain data integrity but enforcing foreign key constraints requires extra lookups on the primary key table to ensure existence. Using ON DELETE CASCADE referential integrity .

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