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缺失索引自动创建语句

【编者按】 本文主要介绍使用系统 SQL 实体自动创建非聚集(non-clustered)索引。作者为意大利软件工程师 GhostHost(笔名)。

本文系OneAPM 工程师编译呈现,以下为正文。

引言

一直以来,关于索引的常见问题是:判断哪部分索引对保证数据库的良好性能是必需的。在本文中,笔者将提供针对该问题的解决方案。本文用例中的所有代码都基于名为 dm_db_missing_index_details 的 SQL Server 系统视图。

背景

在开始安装前,进一步了解 dm_db_missing_index_details 会更有益处。

dm_db_missing_index_details 会返回缺失索引的细节信息。在本文中,我们将更关注以下几列:

  • index_handle :它是一个独特的跨服务器标识符,并且标志一个特定的缺失索引。

  • equality_columns :包含用于相等谓词的所有列

  • inequality_columns :包含用于其他比较的所有列

  • included columns 索引中所包含的查询必要出现列

  • statement : 补充完整索引缺失的表名

实现

本系统的实现基于以下三个实体:

  1. 一个可以计算出待创建索引名称的简单函数

  2. 一个用于简化 dm_db_missing_index_details 的用户视图

  3. 一个为每个索引创建声明的进程

笔者选择将这个系统分为三段进程,但实际上合并存储过程和视图也是可行的。笔者之所以没有选择后一种做法是因为想在创建索引之前先从业务逻辑检查一下存在哪些索引。

使用代码

函数 fn_Index_CreateIndexName

在这个函数中,有三个输入参数:

1.  @equality_columns 2.  @equality_columns 3.  @index_handlE

该函数的目的是为每个期望创建的索引都创建一个唯一名称。

因此,首先拼接 @equality_columns@equality_columns 两个输入变量,如果拼接后所得结果超过120个字符,那就截取至第120个字符。

为什么是120个字符?

因为在SQL Server中,命名最大长度为128个字符。这个函数在 @index_handlE 名字结尾添加字段以便保证唯一的索引名。

CREATE FUNCTION [dbo].[fn_Index_CreateIndexName] (@equality_columns NVARCHAR(4000), _ @Inequality_columns NVARCHAR(4000), @index_handlE INT) RETURNS VARCHAR(128) AS BEGIN  DECLARE @IndexName NVARCHAR(255)  SET @IndexName = ISNULL(@equality_columns,@Inequality_columns)  SET @IndexName = LTRIM(REPLACE(@IndexName,'[','_'))  SET @IndexName = RTRIM(REPLACE(@IndexName,']','_'))  SET @IndexName = REPLACE(@IndexName,',','')  SET @IndexName = REPLACE(@IndexName,'_ _','_')  IF LEN(@IndexName) > 120 BEGIN      SET @IndexName = SUBSTRING(@IndexName,0,120)  END    SET @IndexName = @IndexName + CAST(@index_handlE AS NVARCHAR(15))  RETURN @IndexName  END

视图 vw_Index_MissingIndex

该视图基于 dm_db_missing_index_details 和 sys.databases 表,并使用 fn_Index_CreateIndexName 函数来计算缺失的索引名。

CREATE VIEW [dbo].[vw_Index_MissingIndex] AS  SELECT  '[' + d.name + ']' as DBName,         [dbo].[fn_Index_CreateIndexName]_         (mid.equality_columns,mid.Inequality_columns,mid.index_handlE) AS ID,         REPLACE(mid.equality_columns,',',' ASC,') AS equality_columns,         REPLACE(mid.Inequality_columns,',',' ASC,') AS Inequality_columns,         mid.Included_columns,         mid.[statement] FROM sys.dm_db_missing_index_details mid INNER JOIN sys.databases d on d.database_id = mid.database_id

存储过程 usp_Index_MissingIndexCreationStatements

该存储过程基于 vw_Index_MissingIndex ,并且输出索引创建语句。

CREATE PROCEDURE [dbo].[usp_Index_MissingIndexCreationStatements] AS  DECLARE @IndexCreationPlaceholder_Start  AS NVARCHAR(MAX) DECLARE @IndexCreationPlaceholder_End  AS NVARCHAR(MAX)  -- PREPARE PLACEHOLDER  SET @IndexCreationPlaceholder_Start = 'IF NOT EXISTS(SELECT * _ FROM {2}.sys.indexes WHERE [name] = ''IX_{0}'' )                 BEGIN                 CREATE NONCLUSTERED INDEX [IX_{0}] ON {1}'  SET @IndexCreationPlaceholder_End = ' WITH (PAD_INDEX = OFF, _ STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, _ ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]                 END;' + char(13) + char(10)  -- STATEMENT CREATION  SELECT     DBName,     CASE     WHEN NOT mid.equality_columns IS NULL AND NOT mid.Inequality_columns IS NULL THEN                 REPLACE(REPLACE(REPLACE(@IndexCreationPlaceholder_Start,'{0}', _                 mid.ID),'{1}',mid.[statement]),'{2}',mid.DBName)                 + '                    ( ' +                    COALESCE(mid.equality_columns,'') +                    ' ASC,' +                     COALESCE(mid.Inequality_columns,'') +                    ' ASC                 )' +                 COALESCE('INCLUDE ( ' + mid.Included_columns + ' ) ','')                 + @IndexCreationPlaceholder_End          WHEN mid.equality_columns IS NULL AND NOT mid.Inequality_columns IS NULL THEN                 REPLACE(REPLACE(REPLACE(@IndexCreationPlaceholder_Start,_                 '{0}', mid.ID),'{1}',mid.[statement]),'{2}',mid.DBName)                 + '                    ( ' +                    COALESCE(mid.Inequality_columns,'') +                    ' ASC                 ) ' +                 COALESCE('INCLUDE ( ' + mid.Included_columns + ' ) ','')                 + @IndexCreationPlaceholder_End      WHEN NOT mid.equality_columns IS NULL AND mid.Inequality_columns IS NULL THEN             REPLACE(REPLACE(REPLACE(@IndexCreationPlaceholder_Start,'{0}', _             mid.ID),'{1}',mid.[statement]),'{2}',mid.DBName)             + '                ( ' +            COALESCE(mid.equality_columns,'') +  ' ASC                 ) ' +             COALESCE('INCLUDE ( ' + mid.Included_columns + ' ) ','')             + @IndexCreationPlaceholder_End     ELSE NULL END AS Index_Creation_Statement,     ' DROP INDEX [IX_' + mid.ID  + '] ON ' + mid.[statement]  _     +  + char(13) + char(10) AS Index_Drop_Statement FROM [dbo].[vw_Index_MissingIndex] AS mid

完整代码

-- CREATE FUNCTION fn_Index_CreateIndexName  CREATE FUNCTION [dbo].[fn_Index_CreateIndexName] (@equality_columns NVARCHAR(4000), _ @Inequality_columns NVARCHAR(4000), @index_handlE INT) RETURNS VARCHAR(128) AS BEGIN          DECLAR  E @IndexName NVARCHAR(MAX)      SET @IndexName = ISNULL(@equali  ty_columns,@Inequality_columns)  SET @IndexName = LTRIM(REPLACE(@IndexName,'[','_'))  SET @IndexName = RTRIM(REPLACE(@IndexName,']','_'))  SET @IndexName = REPLACE(@IndexName,',','')  SET @IndexName = REPLACE(@IndexName,'_ _','_')      IF LEN(@IndexName) > 120     BEGIN          SET @IndexName = SUBSTRING(@IndexName,0,120)      END        SET @IndexName = @IndexName + CAST(@index_handlE AS NVARCHAR(15))      RETURN @IndexName  END  GO  -- CREATE FUNCTION vw_Index_MissingIndex  CREATE VIEW [dbo].[vw_Index_MissingIndex]  AS  SELECT  '[' + d.name + ']' as DBName,         [dbo].[fn_Index_CreateIndexName]_         (mid.equality_columns,mid.Inequality_columns,mid.index_handlE) AS ID,         REPLACE(mid.equality_columns,',',' ASC,') AS equality_columns,         REPLACE(mid.Inequality_columns,',',' ASC,') AS Inequality_columns,         mid.Included_columns,         mid.[statement] FROM sys.dm_db_missing_index_details mid INNER JOIN sys.databases d on d.database_id = mid.database_id  GO  CREATE PROCEDURE [dbo].[usp_Index_MissingIndexCreationStatements] AS  DECLARE @IndexCreationPlaceholder_Start  AS NVARCHAR(MAX) DECLARE @IndexCreationPlaceholder_End  AS NVARCHAR(MAX)  -- PREPARE PLACEHOLDER  SET @IndexCreationPlaceholder_Start = 'IF NOT EXISTS_ (SELECT * FROM {2}.sys.indexes WHERE [name] = ''IX_{0}'' )                 BEGIN                 CREATE NONCLUSTERED INDEX [IX_{0}] ON {1}'  SET @IndexCreationPlaceholder_End = ' WITH (PAD_INDEX = OFF, _ STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, _ ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]                 END;' + char(13) + char(10)  -- STATEMENT CREATION  SELECT     DBName,     CASE     WHEN NOT mid.equality_columns IS NULL AND NOT mid.Inequality_columns IS NULL THEN                 REPLACE(REPLACE(REPLACE(@IndexCreationPlaceholder_Start,'{0}', _                 mid.ID),'{1}',mid.[statement]),'{2}',mid.DBName)                 + '                    ( ' +                    COALESCE(mid.equality_columns,'') +                    ' ASC,' +                     COALESCE(mid.Inequality_columns,'') +                    ' ASC                 )' +                 COALESCE('INCLUDE ( ' + mid.Included_columns + ' ) ','')                 + @IndexCreationPlaceholder_End          WHEN mid.equality_columns IS NULL AND NOT mid.Inequality_columns IS NULL THEN                 REPLACE(REPLACE(REPLACE(@IndexCreationPlaceholder_Start,'{0}', _   mid.ID),'{1}',mid.[statement]),'{2}',mid.DBName)             + '                ( ' +                COALESCE(mid.Inequality_columns,'') +                ' ASC             ) ' +             COALESCE('INCLUDE ( ' + mid.Included_columns + ' ) ','')             + @IndexCreationPlaceholder_End      WHEN NOT mid.equality_columns IS NULL AND mid.Inequality_columns IS NULL THEN             REPLACE(REPLACE(REPLACE(@IndexCreationPlaceholder_Start,'{0}', _             mid.ID),'{1}',mid.[statement]),'{2}',mid.DBName)             + '                ( ' +            COALESCE(mid.equality_columns,'') +  ' ASC                 ) ' +             COALESCE('INCLUDE ( ' + mid.Included_columns + ' ) ','')             + @IndexCreationPlaceholder_End     ELSE NULL END AS Index_Creation_Statement, ' DROP INDEX [IX_' + mid.ID  + '] ON ' + mid.[statement]  _     +  + char(13) + char(10) AS Index_Drop_Statement FROM [dbo].[vw_Index_MissingIndex] AS mid  GO

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原文地址: http://www.codeproject.com/Tips/1079651/Automatic-Missing-Non-Clustered-Creation-Statement

原文  http://blog.oneapm.com/apm-tech/634.html
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