SQL Server 2008:处理特定日期边界时查询性能非常慢

Question

对,这是一个奇怪的.

我们有一个Web服务,可以将数据返回给silverlight客户端.使用实体框架针对SQL Server 2008数据库生成查询.这些查询中的大多数都是基于日期范围的 - 例如,在此日期和日期之间拉取结果.此外,视图用于使事情更容易一些.

我们注意到,当发出特定日期或之后开始的特定查询集时,执行将非常缓慢.这个日期是11月5日,任何一年.如果我们的开始日期是提前一天执行将立即执行.所以,5号 - 6号,慢.4 - 6 - 快.

这是EF生成的SQL:

这个查询非常慢(30秒)

SELECT 
1 AS [C1], 
[GroupBy1].[K1] AS [Name], 
[GroupBy1].[A1] AS [C2]
FROM ( SELECT 
[Extent1].[Name] AS [K1], 
SUM([Extent1].[Value]) AS [A1]
FROM (SELECT 
  [view_answers].[Value] AS [Value], 
  [view_answers].[Comment] AS [Comment], 
  [view_answers].[NewStockist] AS [NewStockist], 
  [view_answers].[NewDistPoint] AS [NewDistPoint], 
  [view_answers].[VoucherUsed] AS [VoucherUsed], 
  [view_answers].[CashTotal] AS [CashTotal], 
  [view_answers].[AnswerType] AS [AnswerType], 
  [view_answers].[StartTime] AS [StartTime], 
  [view_answers].[ActualEndTime] AS [ActualEndTime], 
  [view_answers].[Complete] AS [Complete], 
  [view_answers].[UserID] AS [UserID], 
  [view_answers].[UserName] AS [UserName], 
  [view_answers].[QuestionType] AS [QuestionType], 
  [view_answers].[ProductSKU] AS [ProductSKU], 
  [view_answers].[BrandID] AS [BrandID], 
  [view_answers].[TeamID] AS [TeamID], 
  [view_answers].[Name] AS [Name], 
  [view_answers].[Stage] AS [Stage], 
  [view_answers].[Question] AS [Question]
  FROM [dbo].[view_answers] AS [view_answers]) AS [Extent1]
  WHERE 
     ([Extent1].[UserID] = '16E3692F-806E-40A0-BB99-ABBBCC13060D') 
     AND (N'Distribution Points' = [Extent1].[QuestionType]) 
     AND ([Extent1].[StartTime] >= '11/05/2009 00:00:00') 
     AND ([Extent1].[StartTime] <= '11/08/2009 00:00:00') 
     AND (1 = [Extent1].[Complete]) 
     AND (2 = [Extent1].[BrandID]) 
     AND (N'Distribution Points' = [Extent1].[QuestionType])
  GROUP BY 
     [Extent1].[Name])  
  AS [GroupBy1]

这一个会更快

    SELECT 
    1 AS [C1], 
    [GroupBy1].[K1] AS [Name], 
    [GroupBy1].[A1] AS [C2]
    FROM ( SELECT 
    [Extent1].[Name] AS [K1], 
    SUM([Extent1].[Value]) AS [A1]
    FROM (SELECT 
      [view_answers].[Value] AS [Value], 
      [view_answers].[Comment] AS [Comment], 
      [view_answers].[NewStockist] AS [NewStockist], 
      [view_answers].[NewDistPoint] AS [NewDistPoint], 
      [view_answers].[VoucherUsed] AS [VoucherUsed], 
      [view_answers].[CashTotal] AS [CashTotal], 
      [view_answers].[AnswerType] AS [AnswerType], 
      [view_answers].[StartTime] AS [StartTime], 
      [view_answers].[ActualEndTime] AS [ActualEndTime], 
      [view_answers].[Complete] AS [Complete], 
      [view_answers].[UserID] AS [UserID], 
      [view_answers].[UserName] AS [UserName], 
      [view_answers].[QuestionType] AS [QuestionType], 
      [view_answers].[ProductSKU] AS [ProductSKU], 
      [view_answers].[BrandID] AS [BrandID], 
      [view_answers].[TeamID] AS [TeamID], 
      [view_answers].[Name] AS [Name], 
      [view_answers].[Stage] AS [Stage], 
      [view_answers].[Question] AS [Question]
      FROM [dbo].[view_answers] AS [view_answers]) AS [Extent1]
    WHERE 
       ([Extent1].[UserID] = '16E3692F-806E-40A0-BB99-ABBBCC13060D') 
       AND (N'Distribution Points' = [Extent1].[QuestionType]) 
       AND ([Extent1].[StartTime] >= '11/04/2009 00:00:00') 
       AND ([Extent1].[StartTime] <= '11/08/2009 00:00:00') 
       AND (1 = [Extent1].[Complete]) 
       AND (2 = [Extent1].[BrandID]) 
       AND (N'Distribution Points' = [Extent1].[QuestionType])
    GROUP BY 
       [Extent1].[Name])  
    AS [GroupBy1]

如果我们将开始日期设定为去年11月5日,执行将会缓慢,去年11月4日,再次快速.查看数据库中的数据,在第5天没有什么不寻常的.此外,似乎开始日期在5日之后的查询将运行缓慢.

我很难过!

(数据库是远程托管的,所以我没有直接访问它)

UPDATE

感谢thr回复的家伙们.首先,我应该说清楚我对sql server的了解很深.我构建了不同质量的数据库,然后使用Linq To SQL或EF等方法来处理它们.所以我觉得这里有点深度.

关于连接 - 我查询的视图确实包括来自大约6-7个表的数据.我将在下次工作时尝试获取一些统计数据,并在此处添加更多信息.我真的不太了解执行计划,或者他是我可以通过SQL Server Management Studio看到的

从慢查询更新统计信息(受影响的3行)

Table 'tblProducts'. Scan count 0, logical reads 22, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblQuestionTypes'. Scan count 0, logical reads 1496, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblQuestions'. Scan count 0, logical reads 1496, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblSessions'. Scan count 0, logical reads 28551, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblAnswers'. Scan count 1, logical reads 1976256, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblCalls'. Scan count 1, logical reads 439, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblUsers'. Scan count 0, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

来自快速查询的统计信息

Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblAnswers'. Scan count 1, logical reads 7008, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblProducts'. Scan count 0, logical reads 22, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblQuestions'. Scan count 1, logical reads 4, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblQuestionTypes'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblCalls'. Scan count 1, logical reads 439, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblSessions'. Scan count 1, logical reads 47, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblUsers'. Scan count 0, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

更新 查询执行计划(对我来说是一件新事)建议我在其中一个表中添加一个新索引 - 在answers表中的questionid.建议的sql如下:

USE [brandfourcoke]
GO
CREATE NONCLUSTERED INDEX [<Name of Missing Index, sysname,>]
ON [dbo].[tblAnswers] ([QuestionID])
INCLUDE ([CallID],[Value])
GO

查询成本的估计改进为93%.我应该继续这样做吗？该数据库处于实时环境中,并使用sql server 2008的更改跟踪和同步框架.因此我总是担心数据库更改会影响跟踪数据并破坏客户端的内容.是否会添加索引重置更改跟踪数据？谢谢你们的帮助.我觉得这里是一个完全的初学者.

Answer 1

运行慢速和快速查询,SET sTATISTICS IO ON并查看两者之间的逻辑读取/物理读取量是否存在显着差异.

最有可能的是数据存在严重偏差.例如,快速计划上的计划由10行的结果驱动嵌套循环(导致10次嵌套查找),而慢速计划突然看到前一次看到10行的10000行,导致10000次查找.虽然您的查询没有连接,但引擎可能会使用各种访问索引并使用群集索引连接索引.实际执行计划将始终清楚地显示正在发生的事情.