SQL Server查询性能 – 聚簇索引查找

2023年7月13日 222次阅读

请原谅长篇文章,但下面我已经包含了一个完整的脚本来生成和填充我的测试工具.

我的测试工具有以下表格

|--------|  |-------------|  |-----|  |--------------|
|Column  |  |ColumnValue  |  |Row  |  |RowColumnValue|
|--------|  |-------------|  |-----|  |--------------|
|ColumnId|  |ColumnValueId|  |RowId|  |RowId         |
|Name    |  |ColumnId     |  |Name |  |ColumnValueId |
|--------|  |Value        |  |-----|  |--------------|
            |-------------|

它们表示表中的行和列.列中单元格的可能值存储在ColumnValue中.行的选定值存储在RowColumnValue中. (我希望很清楚)

我已经使用10列,10,000行,每列50列值(500)和每行25个选定列值(250,000)填充数据.

我有一些动态sql,它返回所有行,与列一起旋转,并包含每列所选列值的XML列表.

注意：出于性能测试的目的,我将查询包装在SELECT COUNT(*)中,以便查询不会通过网络返回大量数据.

我的测试工具在大约5-6秒内运行此查询(带计数).执行计划显示92％的查询花费在[ColumnValue]上的Clustered Index Seek上.[PK_ColumnValue].客户端统计信息显示客户端处理时间,服务器上的总执行时间和等待时间全部为0.

我意识到RowColumnValue表中的250k行非常多,而且我可能对SQL Server抱有太多期望.但是,我的期望是查询应该能够比这更快地运行.或者至少执行计划应该呈现一个不同的瓶颈,而不是集群索引寻求.

任何人都可以对这个问题有所了解,或者就如何提高效率给我一些建议？

运行数据透视表以显示表的动态SQL：

DECLARE @columnDataList NVARCHAR(MAX)
SELECT
    @columnDataList = 
    CAST
    (
        (
            SELECT
                ', CONVERT(xml, [PVT].[' + [Column].[Name] + ']) [Column.' + [Column].[Name] + ']'
            FROM
                [Column]
            ORDER BY
                [Column].[Name]
            FOR XML PATH('')
        ) AS XML
    ).value('.', 'NVARCHAR(MAX)')

DECLARE @columnPivotList NVARCHAR(MAX)
SELECT
    @columnPivotList = 
    CAST
    (
        (
            SELECT
                ', [' + [Column].[Name] + ']'
            FROM
                [Column]
            ORDER BY
                [Column].[Name]
            FOR XML PATH('')
        ) AS XML
    ).value('.', 'NVARCHAR(MAX)')

EXEC('
    SELECT
        COUNT(*)
    FROM
    (
        SELECT
            [PVT].[RowId]
            ' + @columnDataList + '
        FROM
        (
            SELECT
                [Row].[RowId],
                [Column].[Name] [ColumnName],
                [XmlRowColumnValues].[XmlRowColumnValues] [XmlRowColumnValues]
            FROM
                [Row]
            CROSS JOIN
                [Column]
            CROSS APPLY
            (
                SELECT
                    [ColumnValue].[Value] [Value]
                FROM
                    [RowColumnValue]
                INNER JOIN
                    [ColumnValue]
                ON
                    [ColumnValue].[ColumnValueId] = [RowColumnValue].[ColumnValueId]
                WHERE
                    [RowColumnValue].[RowId] = [Row].[RowId]
                AND
                    [ColumnValue].[ColumnId] = [Column].[ColumnId]
                FOR XML PATH (''''), ROOT(''Values'')
            ) [XmlRowColumnValues] ([XmlRowColumnValues])
        ) [PivotData]
        PIVOT
        (
            MAX([PivotData].[XmlRowColumnValues])
        FOR
            [ColumnName]
            IN
            ([0]' + @columnPivotList + ')
        ) PVT
    ) RowColumnData
')

生成和填充数据库的脚本：

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Row](
    [RowId] [int] IDENTITY(1,1) NOT NULL,
    [Name] [nvarchar](50) NOT NULL,
 CONSTRAINT [PK_Row] PRIMARY KEY CLUSTERED 
(
    [RowId] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Column](
    [ColumnId] [int] IDENTITY(1,1) NOT NULL,
    [Name] [nvarchar](50) NOT NULL,
 CONSTRAINT [PK_Column] PRIMARY KEY CLUSTERED 
(
    [ColumnId] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[RowColumnValue](
    [RowId] [int] NOT NULL,
    [ColumnValueId] [int] NOT NULL,
 CONSTRAINT [PK_RowColumnValue] PRIMARY KEY CLUSTERED 
(
    [RowId] ASC,
    [ColumnValueId] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[ColumnValue](
    [ColumnValueId] [int] IDENTITY(1,1) NOT NULL,
    [ColumnId] [int] NOT NULL,
    [Value] [nvarchar](50) NOT NULL,
 CONSTRAINT [PK_ColumnValue] PRIMARY KEY CLUSTERED 
(
    [ColumnValueId] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
CREATE NONCLUSTERED INDEX [FKIX_ColumnValue_ColumnId] ON [dbo].[ColumnValue] 
(
    [ColumnId] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
GO
ALTER TABLE [dbo].[ColumnValue]  WITH CHECK ADD  CONSTRAINT [FK_ColumnValue_Column] FOREIGN KEY([ColumnId])
REFERENCES [dbo].[Column] ([ColumnId])
GO
ALTER TABLE [dbo].[ColumnValue] CHECK CONSTRAINT [FK_ColumnValue_Column]
GO
ALTER TABLE [dbo].[RowColumnValue]  WITH CHECK ADD  CONSTRAINT [FK_RowColumnValue_ColumnValue] FOREIGN KEY([ColumnValueId])
REFERENCES [dbo].[ColumnValue] ([ColumnValueId])
GO
ALTER TABLE [dbo].[RowColumnValue] CHECK CONSTRAINT [FK_RowColumnValue_ColumnValue]
GO
ALTER TABLE [dbo].[RowColumnValue]  WITH CHECK ADD  CONSTRAINT [FK_RowColumnValue_Row] FOREIGN KEY([RowId])
REFERENCES [dbo].[Row] ([RowId])
GO
ALTER TABLE [dbo].[RowColumnValue] CHECK CONSTRAINT [FK_RowColumnValue_Row]
GO

DECLARE @columnLoop INT
DECLARE @columnValueLoop INT
DECLARE @rowLoop INT

DECLARE @columnId INT
DECLARE @columnValueId INT
DECLARE @rowId INT

SET @columnLoop = 0

WHILE @columnLoop < 10
BEGIN

    INSERT INTO [Column] ([Name]) VALUES(NEWID())

    SET @columnId = @@IDENTITY

    SET @columnValueLoop = 0

    WHILE @columnValueLoop < 50
    BEGIN

        INSERT INTO [ColumnValue] ([ColumnId], [Value]) VALUES(@columnId, NEWID())

        SET @columnValueLoop = @columnValueLoop + 1

    END

    SET @columnLoop = @columnLoop + 1

END

SET @rowLoop = 0

WHILE @rowLoop < 10000
BEGIN

    INSERT INTO [Row] ([Name]) VALUES(NEWID())

    SET @rowId = @@IDENTITY

    INSERT INTO [RowColumnValue] ([RowId], [ColumnValueId]) SELECT TOP 25 @rowId, [ColumnValueId] FROM [ColumnValue] ORDER BY NEWID()

    SET @rowLoop = @rowLoop + 1

END

最佳答案 我同意@marc_s和@KM这个宏伟的设计从一开始就注定要失败.

数以百万计的微软开发人员已经开始构建和微调强大而强大的数据库引擎,但是你将通过将所有内容塞入少量通用表并重新实现SQL Server已经完成的所有内容来重新创建它们.专为您而设计.

SQL Server已经包含包含实体名称,列名称等的表.您通常不直接与这些系统表交互的事实是一件好事：它被称为抽象.并且你不太可能比SQL Server更好地实现抽象.

在一天结束时,用你的方法(a)即使是最简单的查询也是怪异的; (b)你永远不会接近最佳性能,因为你放弃了所有你免费获得的查询优化.

如果不了解您的应用程序或您的要求,很难提供任何具体的建议.但我建议一些好的旧标准化会有很长的路要走.任何执行良好,非平凡的数据库都有很多表;十个表加上十个xtab表不应该吓跑你.

并且不要害怕SQL代码生成作为跨不同表实现公共接口的方式.有点可以走很长的路.

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