【发布时间】：2012-05-10 00:02:56
【问题描述】：
我有一个相当复杂的查询，一旦 SQL Server 建立了查询计划（令人满意），它会在不到一秒的时间内运行。然而，根据分析器，查询第一次运行 ShowPlanXML 事件大约需要 14 秒（不令人满意）。
有什么方法可以优化 ShowPlanXML 以使其在第一次运行时更快地完成？
或者我要创建一个计划指南？
这里的信息是 SQL 查询（由 NHibernate 生成）：
SELECT top 20 this_.UserId as UserId55_0_, this_.User_Version as User2_55_0_, this_.User_ApplicationId as User3_55_0_, this_.User_DeletedOn as User4_55_0_, this_.User_CreatedOn as User5_55_0_, this_.User_ModifiedOn as User6_55_0_, this_.User_CreatedById as User7_55_0_, this_.User_CreatedByName as User8_55_0_, this_.User_ModifiedById as User9_55_0_, this_.User_ModifiedByName as User10_55_0_, this_.User_Name as User11_55_0_, this_.User_ExternalId as User12_55_0_, this_.User_DynamicFields as User13_55_0_,
this_.User_FirstName as User14_55_0_, this_.User_LastName as User15_55_0_, this_.User_Prefix as User16_55_0_, this_.User_Gender as User17_55_0_, this_.User_Language as
User18_55_0_, this_.User_Code as User19_55_0_, this_.User_Nationality as User20_55_0_, this_.User_FirstLanguage as User21_55_0_, this_.User_DrivingLicence as User22_55_0_,
this_.User_Category as User23_55_0_, this_.User_UserStatus as User24_55_0_, this_.User_UserType as User25_55_0_, this_.User_WorkPhone as User26_55_0_, this_.User_MobilePhone as
User27_55_0_, this_.User_Fax as User28_55_0_, this_.User_Mail as User29_55_0_, this_.User_Login as User30_55_0_, this_.User_Password as User31_55_0_, this_.User_BornOn as
User32_55_0_, this_.User_StartedOn as User33_55_0_, this_.User_FinishedOn as User34_55_0_, this_.User_Address as User35_55_0_, this_.User_PostalCode as User36_55_0_,
this_.User_City as User37_55_0_, this_.User_Country as User38_55_0_, this_.User_PositionTitle as User39_55_0_, this_.User_Comments as User40_55_0_, this_.User_OptionalField1 as
User41_55_0_, this_.User_OptionalField2 as User42_55_0_, this_.User_OptionalField3 as User43_55_0_, this_.User_PasswordConsecutiveFailedAttempts as User44_55_0_,
this_.User_PasswordModificationDate as User45_55_0_, this_.User_WrongPasswordAttemptDate as User46_55_0_, this_.User_PictureUrl as User47_55_0_, this_.User_PasswordModificationStatus as User48_55_0_, this_.User_SecretQuestionConsecutiveFailedAttempts as User49_55_0_, this_.User_PlatformMailTransfer as User50_55_0_, this_.User_TimeZoneId as User51_55_0_, this_.User_ConnectionState as User52_55_0_, this_.User_LastConnectionId as User53_55_0_, this_.User_TotalPercentRealized as User54_55_0_
FROM Dir_User this_
WHERE this_.UserId in (
SELECT distinct this_0_.UserId as y0_
FROM Dir_User this_0_ inner join Dir_UserDynamicGroup dynamicgro3_ on this_0_.UserId=dynamicgro3_.UsDy_UserId
inner join Dir_Group dynamicgro1_ on dynamicgro3_.UsDy_DynamicGroupId=dynamicgro1_.GroupId
WHERE dynamicgro1_.GroupId = (51904517)
and this_0_.User_ApplicationId = 65536
and this_0_.User_DeletedOn is null
and this_0_.UserId in (
SELECT distinct this_0_0_.TargetUserId as y0_
FROM Dir_UserGroupMember this_0_0_
WHERE this_0_0_.OwnerUserId = 7341195
and ( (this_0_0_.Scope & 139280) != 0 or ( (this_0_0_.Scope & 139280) != 0
and this_0_0_.GroupId = this_0_0_.SubGroupId))))
ORDER BY this_.User_Name asc
【问题讨论】：
-
您是说查询由于编译而第一次执行需要很长时间才能执行，或者实际上显示计划需要很长时间？如果是后者，我说不用担心；您不会在应用程序中运行查询并带回显示计划结果。它是一种诊断工具，仅用于调整和故障排除。
-
是前者 - 根据分析器，每次在 SSMS 中执行查询时都会运行 ShowPlanXml 事件。第一次编译需要 14 秒，然后从缓存中访问计划。如果我运行 DBCC DROPCLEANBUFFERS 缓存将被清除并重新计算计划需要 14 秒
-
据此 (msdn.microsoft.com/en-us/library/ms188661.aspx)，每次查询运行时都会触发该事件，并且我引用“包含此事件类的跟踪可能会导致显着的性能开销”。如果您想查看查询的性能，我建议您查看 DMV，即 sys.dm_exec_query_stats 及其兄弟。
标签： sql-server sql-server-2008 sql-execution-plan