Missing Indexes in SQL Server 2005-白红宇

There are several new features in SQL Server 2005. There are a few features to help find missing indexes, which are some of the very good ones. How great it will be if you know what indexes you need to create based on your workload? In SQL Server 2000, we had to use SQL Profiler trace files and Index tuning wizard. But with SQL Server 2005 DMVs, we can easily figure out what indexes we need to create which would benefit our application.

The following are the missing index DMVs ( From SQL Server 2005 BOL)

sys.dm_db_missing_index_group_stats	Returns summary information about missing index groups, for example, the performance improvements that could be gained by implementing a specific group of missing indexes.
sys.dm_db_missing_index_groups	Returns information about a specific group of missing indexes, such as the group identifier and the identifiers of all missing indexes that are contained in that group.
sys.dm_db_missing_index_details	Returns detailed information about a missing index; for example, it returns the name and identifier of the table where the index is missing, and the columns and column types that should make up the missing index.
sys.dm_db_missing_index_columns	Returns information about the database table columns that are missing an index.

Let’s see what indexes are there for table [Person.Address] table in AdventureWorks database by running this code:

use

AdventureWorks;

exec

sp_helpindex

[

Person.Address

]

Fig:1

I don’t see an index for ModifiedDate column for [Person.Address] table. So, to get a entry in the “sys.dm_db_missing_index_details” DMV, lets run a query like this:

Query: 1

select

from

Person.Address

where

ModifiedDate

01/01/2008

You may not see any results for the query above, but SQL Server internally recorded that a query was run and a index on “ModifiedDate” column would have been very useful.

Query: 2

select

from

sys.dm_db_missing_index_details:

Fig: 2

In Fig: 2, see the “equality_columns” field, which implies that a index on the [Modified Date] column is missing ( or might be helpful)

Query: 3:

select

db_name

(d.database_id) dbname,

object_name

(d.

object_id

) tablename, d.index_handle,

d.equality_columns, d.inequality_columns, d.included_columns, d.statement

fully_qualified_object, gs.

from

sys.dm_db_missing_index_groups g

join

sys.dm_db_missing_index_group_stats gs

gs.group_handle

g.index_group_handle

join

sys.dm_db_missing_index_details d

g.index_handle

d.index_handle

where

d.database_id

and

object_id

and

object_name

(d.

object_id

)

Address

Run Query 1 several times. Now, run Query: 3,

Fig: 3

In Fig 3, notice the “user_seeks” column. So every time a query is run, for which an index might be useful, SQL Server keeps updating the missing index DMVs. This is very valuable information, based on this you can create indexes to support those queries. Isn’t this cool! Yes, SQL Server 2005 rocks!

The DMVs for missing indexes are great new features. I work with a Siebel CRM database where queries are built dynamically. So it is hard to design indexes in advance. The missing index feature helps to me create indexes for those queries that have high “user_seeks” for a particular column in a table.

For more information see “About the Missing Indexes Feature” in SQL Server 2005 Books Online.

from：

本文转自 Fanr_Zh 博客园博客，原文链接：http://www.cnblogs.com/Amaranthus/archive/2011/04/02/2003203.html，如需转载请自行联系原作者