前言感想：一时兴起，突然想写一个关于MS SQL的巡检系列方面的文章，因为我觉得这方面的知识分享是有价值，也是非常有意义的。一方面，很多经验不足的人，对于巡检有点茫然，不知道要从哪些方面巡检，另外一方面，网上关于MS SQL巡检方面的资料好像也不是特别多。写这个系列只是一个分享，自己的初衷是一个知识梳理、总结提炼过程，有些知识和脚本也不是原创，文章很多地方也是融入了自己的一些想法和见解的，不足和肤浅之处肯定也非常多，抛砖引玉，也希望大家提意见和建议、补充，指正其中的不足之处。Stay Hungry Stay Foolish！
在SQL Server数据库中，有可能存在重复的索引（Duplicate Indexes），这个不仅影响性能（INSERT、UPDATE、DELETE时带来额外的IO开销，当数据库维护，索引重组时也会带来额外的开销），而且占用空间。数据库存在重复索引（Duplicate Indexes）的原因是多方面的，很多时候、很多事情不是你所能完全掌控的，除非你所管理的数据库非常规范，权限控制、脚本发布非常严格、流程化。暂且不说这些，那么怎么在数据库巡检过程找出这些重复的索引（Duplicate Indexes）呢？ 下面分享一个我在Premier Proactive Services中发现一个的脚本（做了一些修改和调整）。
我们以AdventureWorks2014数据库为例，如下所示，表[Person].[Address]下有4个索引，如下所示
假设某个二愣子在这个表的字段StateProvinceID上创建了下面重复索引，IX_Address_N1 与IX_Address_StateProvinceID是一个重复索引。
CREATE INDEX IX_Address_N1 ON [Person].[Address](StateProvinceID);
那么我们执行下面脚本就能找到这个重复的索引，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 = 聚集列存储索引(SQL 2014~ SQL 2016)
AND i.type <> 6 -- 6 = 非聚集列存储索引(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，关于重复索引（Duplicate Indexes）表示存在的索引除了名字不一样外， 索引所在字段以及索引字段顺序都是一样的。An index is considered to be a duplicate if it references the same column and ordinal position as another index in the same database。 这个脚本是找出一模一样的索引，如果你创建下面索引，索引字段一样，但是有包含列字段不一样，那么这个脚本会将这个索引视为不一样的索引。有兴趣可以自己试试。
CREATE INDEX IX_Address_N2 ON [Person].[Address](StateProvinceID) INCLUDE (City);
另外关于XML索引的重复索引，可以使用下面脚本检查。
--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;
在每个库跑一次这个脚本，就能将所有的重复的索引（Duplicate Indexes）全部找出，但是当手头服务器、数据库特别多时，这个工作也是一个体力活，可以将这个常规工作自动化，避免重复劳动，我将这个集成在MyDBA工具里面，只需要点击一下鼠标，就可以帮助我自动处理这些工作。
