数据库引擎优化顾问期间删除的索引

Question

我正在使用“数据库引擎优化顾问”分析查询。在此期间，数据库开始阻塞，长时间运行的查询并以重新启动实例结束。当我之后检查时，我发现drop index已经执行了一些命令。

drop index [dbo].[Profile].[_dta_index_Profile_7_1563152614__K15_K1]

为什么会这样？我正在调整的查询不在配置文件表上！如何检查此索引之前是否已在系统中或在分析期间创建？

Answer 1

由 DTA 创建和删除的索引很可能是假设索引 - DTA 在运行时创建以执行其分析并且应该（但并不总是）在完成后删除的索引。

即使您不考虑调整该特定表，也可以创建这些假设索引！我建议您直接查询一些系统 DMV以找出缺失的索引。这避免了 DTA 令人讨厌的行为，并为您的索引问题提供了一些更细粒度的见解。

您可以使用SQL Server Central 中的以下查询来检测 DTA 中应删除的任何剩余假设索引。

/*
      -----------------------------------------------------------------
      Hypothetical Indexes
      -----------------------------------------------------------------

      For more SQL resources, check out SQLServer365.blogspot.com

      -----------------------------------------------------------------

      You may alter this code for your own purposes.
      You may republish altered code as long as you give due credit.
      You must obtain prior permission before blogging this code.

      THIS CODE AND INFORMATION ARE PROVIDED "AS IS"

      -----------------------------------------------------------------
*/
-- Set database context
USE master;
GO

-- Declare variables
DECLARE@EmailProfile VARCHAR(255)
DECLARE@EmailRecipient VARCHAR(255)
DECLARE@EmailSubject VARCHAR(255)

-- Set variables
SET@EmailProfile = 'DBA'
SET@EmailRecipient = 'Chris@SQLServer365.com'
SET@EmailSubject = 'ALERT - Hypothetical Indexes found on ' + @@SERVERNAME

-- Drop temporary table if exists
IF OBJECT_ID('tempDB.dbo.#HypotheticalIndexDropScript') IS NOT NULL
    DROP TABLE #HypotheticalIndexDropScript;

-- Create Temporary Table
CREATE TABLE #HypotheticalIndexDropScript
    (
      DatabaseName VARCHAR(255) ,
      HypotheticalIndexDropScript VARCHAR(4000)
    );

INSERT  INTO#HypotheticalIndexDropScript
        EXEC sp_msforeachdb 'USE [?]; SELECT  DB_NAME(DB_ID()), ''USE '' + ''['' + DB_NAME(DB_ID()) + ''];'' + '' IF  EXISTS (SELECT 1 FROM sys.indexes  AS i WHERE i.[object_id] = '' + ''object_id('' + + '''''''' + ''['' + SCHEMA_NAME(o.[schema_id]) + ''].'' + ''['' +  OBJECT_NAME(i.[object_id]) + '']'' + '''''''' + '')'' + '' AND name = '' + '''''''' + i.NAME + '''''''' + '') ''    
       + '' DROP INDEX '' + ''['' + i.name + '']'' + '' ON '' + ''['' + SCHEMA_NAME(o.[schema_id]) + ''].'' + ''['' + OBJECT_NAME(o.[object_id]) + ''];'' AS HypotheticalIndexDropScript
FROM    sys.indexes i
        INNER JOIN sys.objects o ON o.[object_id] = i.[object_id]
WHERE is_hypothetical = 1'

-- Check for hypothetical indexes
IF EXISTS ( SELECT  1
            FROM    #HypotheticalIndexDropScript )
    BEGIN
        DECLARE@tableHTML NVARCHAR(MAX);
        SET@tableHTML = N'<style type="text/css">'
            + N'.h1 {font-family: Arial, verdana;font-size:16px;border:0px;background-color:white;} '
            + N'.h2 {font-family: Arial, verdana;font-size:12px;border:0px;background-color:white;} '
            + N'body {font-family: Arial, verdana;} '
            + N'table{font-size:12px; border-collapse:collapse;border:1px solid black; padding:3px;} '
            + N'td{background-color:#F1F1F1; border:1px solid black; padding:3px;} '
            + N'th{background-color:#99CCFF; border:1px solid black; padding:3px;}'
            + N'</style>' + N'<table border="1">' + N'<tr>'
            + N'<th>DatabaseName</th>'
            + N'<th>HypotheticalIndexDropScript</th>' + N'</tr>'
            + CAST(( SELECT td =DatabaseName ,
                            '' ,
                            td = HypotheticalIndexDropScript ,
                            ''
                     FROM   #HypotheticalIndexDropScript
                   FOR
                     XMLPATH('tr') ,
                         TYPE
                   ) AS NVARCHAR(MAX)) + N'</table>';

            -- Email results
        EXECmsdb.dbo.sp_send_dbmail @profile_name = @EmailProfile,
            @recipients = @EmailRecipient, @subject = @EmailSubject,
            @body =@tableHTML, @body_format = 'HTML';
    END
    GO