为什么我的查询在mgmt studio上运行速度快但在特定参数的应用程序中运行缓慢？

Question

我有这个查询（由实体框架4为MSSQL 2008R2生成）：

SELECT 
[Limit1].[C1] AS [C1], 
[Limit1].[Id] AS [Id], 
[Limit1].[Text] AS [Text], 
[Limit1].[Sender] AS [Sender], 
[Limit1].[Time] AS [Time], 
[Limit1].[Status] AS [Status]
FROM ( SELECT TOP (100) 
    [Extent1].[Id] AS [Id], 
    [Extent1].[Sender] AS [Sender], 
    [Extent1].[Time] AS [Time], 
    [Extent1].[Text] AS [Text], 
    [Extent1].[Status] AS [Status], 
    1 AS [C1]
    FROM [dbo].[MyTable] AS [Extent1]
    WHERE (0 = [Extent1].[DeleteStatus]) 
        AND ([Extent1].[OwnerId] = @p__linq__0) 
        AND (1 = [Extent1].[Cateogry])      
        AND ([Extent1].[Id] > @p__linq__1)
)  AS [Limit1]

-- @p__linq__0=123, @p__linq__1 = 1234

除了具有某些特定参数的查询之外，所有查询都会在不到50毫秒内执行（从应用程序，通过EF）。使用这些参数，尽管结果集返回零行，但查询执行时间超过20秒（每次）。当我在管理工作室中运行相同的查询时，它需要0毫秒。该计划（估计和确切）显示如下：

SQL-Server探查器显示与此对应的查询：

exec sp_executesql N'SELECT 
[Limit1].[C1] AS [C1], 
[Limit1].[Id] AS [Id], 
[Limit1].[Text] AS [Text], 
[Limit1].[Sender] AS [Sender], 
[Limit1].[Time] AS [Time], 
[Limit1].[Status] AS [Status]
FROM ( SELECT TOP (100) 
    [Extent1].[Id] AS [Id], 
    [Extent1].[Sender] AS [Sender], 
    [Extent1].[Time] AS [Time], 
    [Extent1].[Text] AS [Text], 
    [Extent1].[Status] AS [Status], 
    1 AS [C1]
    FROM [dbo].[MyTable] AS [Extent1]
    WHERE (0 = [Extent1].[DeleteStatus]) AND ([Extent1].[OwnerId] = @p__linq__0) AND (1 = [Extent1].[Cateogry]) AND ([Extent1].[Id] > @p__linq__1)
)  AS [Limit1]',N'@p__linq__0 bigint,@p__linq__1 bigint',@p__linq__0=123,@p__linq__1=1234

该表格包含以下相关指数：

PK___1(Id) -- Clustered, Column [Id] is bigint
IX____OwnerId_Category(OwnerId,Category,Status) -- Included-Column: DeleteStatus

这可能是什么原因？我该如何解决？ 顺便说一下：

• 表包含50M +行。
• 统计数据每日更新。
• 当碎片超过20％时，指数会在3/4天内重建。

从其他帖子中读到，我执行了这些（当然没有理解。我只是在寻找快速修复。）：

• DBCC DROPCLEANBUFFERS
• DBCC FREEPROCCACHE

但它完全相同。

Answer 1

评论中的链接很棒：1）Slow in the Application, Fast in SSMS和2）The Elephant and the Mouse, or, Parameter Sniffing in SQL Server

不是我理解所有这些;但我通过将动态SQL转换为使用索引提示的存储过程来摆脱这种情况。