TAILIEUCHUNG - Microsoft SQL Server 2008 R2 Unleashed- P148

Microsoft SQL Server 2008 R2 Unleashed- P148: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 | 1414 CHAPTER 38 Database Design and Performance which in turn reduces the number of I Os on the table. Vertical splitting is a method of reducing the width of a table by splitting the columns of the table into multiple tables. Usually all frequently used columns are kept in one table and others are kept in the other table. This way more records can be accommodated per page fewer I Os are generated and more data can be cached into SQL Server memory. Figure illustrates a vertically partitioned table. The frequently accessed columns of the authors table are stored in the author_primary table whereas less frequently used columns are stored in the author_secondary table. Authors Author_primary Au_id Au_Iname Au_fname SocialSec BirthDate Homephone Workphone Cellphone Addrl Addr2 City Zip State Au_id Au_Iname Au_fname SocialSec Author_secondary Au_id BirthDate Homephone Workphone Cellphone Addrl Addr2 City Zip State FIGURE Vertical partitioning of data. TIP Make the decision to split data very carefully especially when the system is already in production. Changing the data structure might have a system-wide impact on a large number of queries that reference the old definition of the object. In such cases to minimize risks you might want to use SQL Server views to hide the vertical partitioning of data. Also if you find that users and developers are frequently joining between the vertically split tables because they need to pull data together from the two tables you might want to reconsider the split point or the splitting of the table itself. Doing frequent joins between split tables with smaller rows requires more I Os to retrieve the same data than if the data resided in a single table with wider rows. Database Filegroups and Performance 1415 Performance Implications of Zero-to-One Relationships Suppose that one of the development managers in your company Bob approaches you to discuss some database schema changes. He is one of several managers whose groups all

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