2. 计算机
  3. You are the administrator of SQL Server 2000 computer. The server contains a database named Inventory. The database has a set of

You are the administrator of SQL Server 2000 computer. The server contains a database named Inventory. The database has a set of

admin2009-05-19  22
问题 You are the administrator of SQL Server 2000 computer. The server contains a database named Inventory. The database has a set of tables that track the location of parts. The tables are configured as shown in the Database Schema exhibit.


You examine the indexes in the PartsLocations table. The indexes are configured as shown in the Indexes exhibit.


You also examine the contiguity of the PK_partsLocations index and receive the following results:

DBCC SHOWCONTIG scanning ’PartsLocations’ table...
Table: ’PartsLocations’ (1); index ID: 1, database ID: 6
TABLE level scan performed.
- Pages Scanned................................: 3000
- Extents Scanned..............................: 750
- Extent Switches..............................: 502
- Avg. Pages per Extent........................: 4.0
- Scan Density [Best Count:Actual Count].......: 33.33% [1:3]
- Logical Scan Fragmentation...................: 33.33%
- Extent Scan Fragmentation....................: 33.33%
- Avg. Bytes Free per Page.....................: 1166.0
- Avg. Page Density (full).....................: 85.77%

You need to improve the performance of the queries that join this table to the Parts table and the Locations table. What should you do?
选项 A、Re-create the PK_PartsLocations index as a clustered index.
B、Re-create the IX_PartsLocations_PartsID as a clustered index.
C、Re-create the IX_PartsLocations_LocationId as a clustered index.
D、Re-create the PK_PartsLocations index as a nonclustered index.
答案A
解析 Explanation:The output of the DBCC SHOWCONTIG shows that the clustered index of the table is fragmented. Both Logical Scan Fragmentation and Extent Scan Fragmentation are above 10%. The clustered index PK_PartsLocations should be rebuilt.

Note: In general, you need to do very little in terms of index maintenance. However, indexes can become fragmented. You can use the DBCC SHOWCONTIG command to report on the fragmentation of an index.

You can use either the Extent Scan Fragmentation value or the Logical Scan Fragmentation value to determine the general level of fragmentation in a table. Logical Scan Fragmentation and, to a lesser extent, Extent Scan Fragmentation values give the best indication of a table’s fragmentation level. Both these values should be as close to zero as possible (although a value from 0% through 10% may be acceptable).

Incorrect Answers:
B, C: There already exists a clustered index, the PK_PartsLocations index. A table can only contain one clustered index.

D: A clustered index is faster that a non-clustered index. We should rebuild the clustered index, not create a nonclustered index instead.
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