前言感想：一時興起，突然想寫一個關於MS SQL的巡檢系列方面的文章，因為我覺得這方面的知識分享是有價值，也是非常有意義的。一方面，很多經驗不足的人，對於巡檢有點茫然，不知道要從哪些方面巡檢，另外一方面，網上關於MS SQL巡檢方面的資料好像也不是特別多。寫這個系列只是一個分享，自己的初衷是一個知識梳理、總結提煉過程，有些知識和腳本也不是原創，文章很多地方也是融入了自己的一些想法和見解的，不足和膚淺之處肯定也非常多，拋磚引玉，也希望大家提意見和建議、補充，指正其中的不足之處。Stay Hungry Stay Foolish！
在SQL Server數據庫中，有可能存在重復的索引（Duplicate Indexes），這個不僅影響性能（INSERT、UPDATE、DELETE時帶來額外的IO開銷，當數據庫維護，索引重組時也會帶來額外的開銷），而且占用空間。數據庫存在重復索引（Duplicate Indexes）的原因是多方面的，很多時候、很多事情不是你所能完全掌控的，除非你所管理的數據庫非常規范，權限控制、腳本發布非常嚴格、流程化。暫且不說這些，那么怎么在數據庫巡檢過程找出這些重復的索引（Duplicate Indexes）呢？ 下面分享一個我在Premier Proactive Services中發現一個的腳本（做了一些修改和調整）。
我們以AdventureWorks2014數據庫為例，如下所示，表[Person].[Address]下有4個索引，如下所示
假設某個二愣子在這個表的字段StateProvinceID上創建了下面重復索引，IX_Address_N1 與IX_Address_StateProvinceID是一個重復索引。
CREATE INDEX IX_Address_N1 ON [Person].[Address](StateProvinceID);
那么我們執行下面腳本就能找到這個重復的索引，如下所示
;WITH IndexColumns
AS ( SELECT DISTINCT
SCHEMA_NAME(o.schema_id) AS SchemaName ,
OBJECT_NAME(o.object_id) AS TableName ,
i.name AS IndexName ,
o.object_id AS [Object_ID] ,
i.index_id AS Index_ID ,
i.type_desc AS IndexType ,
( SELECT CASE key_ordinal
WHEN 0 THEN NULL
ELSE '[' + COL_NAME(k.object_id,
column_id) + '] '
+ CASE WHEN is_descending_key = 1
THEN 'Desc'
ELSE 'Asc'
END
END AS [data()]
FROM sys.index_columns k WITH(NOLOCK)
WHERE k.object_id = i.object_id
AND k.index_id = i.index_id
ORDER BY key_ordinal ,
column_id
FOR
XML PATH('')
) AS IndexColumns ,
CASE WHEN i.index_id = 1
THEN ( SELECT '[' + name + ']' AS [data()]
FROM sys.columns (NOLOCK) AS c
WHERE c.object_id = i.object_id
AND c.column_id NOT IN (
SELECT column_id
FROM sys.index_columns (NOLOCK)
AS kk
WHERE kk.object_id = i.object_id
AND kk.index_id = i.index_id )
ORDER BY column_id
FOR
XML PATH('')
)
ELSE ( SELECT '[' + COL_NAME(k.object_id,
column_id) + ']' AS [data()]
FROM sys.index_columns k WITH(NOLOCK)
WHERE k.object_id = i.object_id
AND k.index_id = i.index_id
AND is_included_column = 1
AND k.column_id NOT IN (
SELECT column_id
FROM sys.index_columns kk
WHERE k.object_id = kk.object_id
AND kk.index_id = 1 )
ORDER BY key_ordinal ,
column_id
FOR
XML PATH('')
)
END AS IndexInclude
FROM sys.indexes i WITH(NOLOCK)
INNER JOIN sys.objects o WITH(NOLOCK) ON i.object_id = o.object_id
INNER JOIN sys.index_columns ic WITH(NOLOCK ) ON ic.object_id = i.object_id
AND ic.index_id = i.index_id
INNER JOIN sys.columns c WITH(NOLOCK) ON c.object_id = ic.object_id
AND c.column_id = ic.column_id
WHERE o.type = 'U'
AND i.index_id <> 0 -- 0 = 堆
AND i.type <> 3 -- 3 = XML
AND i.type <> 5 -- 5 = 聚集列存儲索引(SQL 2014~ SQL 2016)
AND i.type <> 6 -- 6 = 非聚集列存儲索引(SQL 2014~ SQL 2016)
AND i.type <> 7 -- 7 = 非聚集哈希索引(SQL 2014~ SQL 2016)
GROUP BY o.schema_id ,
o.object_id ,
i.object_id ,
i.name ,
i.index_id ,
i.type_desc
),
DuplicatesTable
AS ( SELECT ic1.SchemaName ,
ic1.TableName ,
ic1.IndexName ,
ic1.[Object_ID] ,
ic2.IndexName AS DuplicateIndexName ,
ic1.IndexType ,
CASE WHEN ic1.index_id = 1
THEN ic1.IndexColumns + ' (Clustered)'
WHEN ic1.IndexInclude = '' THEN ic1.IndexColumns
WHEN ic1.IndexInclude IS NULL THEN ic1.IndexColumns
ELSE ic1.IndexColumns + ' INCLUDE ' + ic1.IndexInclude
END AS IndexCols ,
ic1.index_id
FROM IndexColumns ic1
JOIN IndexColumns ic2 ON ic1.object_id = ic2.object_id
AND ic1.index_id < ic2.index_id
AND ic1.IndexColumns = ic2.IndexColumns
AND ( ISNULL(ic1.IndexInclude, '') = ISNULL(ic2.IndexInclude,
'')
OR ic1.index_id = 1
)
)
SELECT SchemaName ,
TableName ,
IndexName ,
DuplicateIndexName ,
IndexType,
IndexCols ,
Index_ID ,
Object_ID ,
0 AS IsXML
FROM DuplicatesTable dt
ORDER BY 1 , 2 ,3
注意，關於重復索引（Duplicate Indexes）表示存在的索引除了名字不一樣外， 索引所在字段以及索引字段順序都是一樣的。An index is considered to be a duplicate if it references the same column and ordinal position as another index in the same database。 這個腳本是找出一模一樣的索引，如果你創建下面索引，索引字段一樣，但是有包含列字段不一樣，那么這個腳本會將這個索引視為不一樣的索引。有興趣可以自己試試。
CREATE INDEX IX_Address_N2 ON [Person].[Address](StateProvinceID) INCLUDE (City);
另外關於XML索引的重復索引，可以使用下面腳本檢查。
--Use the below T-SQL script to generate the complete list of duplicate XML indexes in a given database:
;WITH XMLTable
AS ( SELECT OBJECT_NAME(x.object_id) AS TableName ,
SCHEMA_NAME(o.schema_id) AS SchemaName ,
x.object_id ,
x.name ,
x.index_id ,
x.using_xml_index_id ,
x.secondary_type ,
CONVERT(NVARCHAR(MAX), x.secondary_type_desc) AS secondary_type_desc ,
ic.column_id
FROM sys.xml_indexes x ( NOLOCK )
JOIN sys.objects o ( NOLOCK ) ON x.object_id = o.object_id
JOIN sys.index_columns (NOLOCK) ic ON x.object_id = ic.object_id
AND x.index_id = ic.index_id
),
DuplicatesXMLTable
AS ( SELECT x1.SchemaName ,
x1.TableName ,
x1.name AS IndexName ,
x2.name AS DuplicateIndexName ,
x1.secondary_type_desc AS IndexType ,
x1.index_id ,
x1.object_id ,
ROW_NUMBER() OVER ( ORDER BY x1.SchemaName, x1.TableName, x1.name, x2.name ) AS seq1 ,
ROW_NUMBER() OVER ( ORDER BY x1.SchemaName DESC, x1.TableName DESC, x1.name DESC, x2.name DESC ) AS seq2 ,
NULL AS inc
FROM XMLTable x1
JOIN XMLTable x2 ON x1.object_id = x2.object_id
AND x1.index_id < x2.index_id
AND x1.using_xml_index_id = x2.using_xml_index_id
AND x1.secondary_type = x2.secondary_type
)
SELECT SchemaName ,
TableName ,
IndexName ,
DuplicateIndexName ,
IndexType ,
Index_ID ,
[Object_ID] ,
1 AS IsXML
FROM DuplicatesXMLTable dtxml
ORDER BY 1 ,
2 ,
3;
在每個庫跑一次這個腳本，就能將所有的重復的索引（Duplicate Indexes）全部找出，但是當手頭服務器、數據庫特別多時，這個工作也是一個體力活，可以將這個常規工作自動化，避免重復勞動，我將這個集成在MyDBA工具里面，只需要點擊一下鼠標，就可以幫助我自動處理這些工作。