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Accepted
Antyan
Asked: 2022-06-16 06:38:44 +0800 CST

数据仓库和数据湖更新的最佳索引策略

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我们有一个 sql server 数据库，用作数据湖和数据仓库。数据库中的每个表都有一些标准化的定义，因为我们现在有 600 个左右的表，因此维护需要在某种程度上自动化。

加载每个表的一般过程是首先将表的副本加载到 changeLog 模式中的哈希表中（如果我们可以确定更改的记录是什么，有时只加载更改的记录），然后将 changeLog 表与目标表进行比较桌子。目标表用于报告，因此这种 changeLog 方法允许我们持久化目标表并仅应用最少的 UPDATE/INSERT 操作。

每个目标表都有一个唯一键/业务键，可通过配置表识别，并具有在每个表中命名相同的标准化审计列。审计专栏告诉我们

  1. 当记录被添加到数据仓库时
  2. 上次在数据仓库中更新记录的时间
  3. 记录是否已在源中删除
  4. 使用 HASHBYTES('SHA2_256', CONCAT()) 更改的记录标识符

更改后的记录标识符曾经是 CHECKSUM()，但我们发现 CHECKSUM() 的冲突率太高而无法信任。我刚刚在每个表中添加了一个 HASHBYTES() 列并填充了它。

我将 HASHBYTES() 列创建为 VARBINARY(MAX)。现在，每次加载表时，我们可以通过将在 changeLog 表中计算的新 HASHBYTES() 值与目标表中的持久值进行比较来判断是否需要更新记录。

我立即注意到从 INT CHECKSUM() 切换到 VARBINARY(MAX) HASHBYTES() 导致更新检查过程显着减慢。我在每个 CHECKSUM 列上都有 NONCLUSTERED 索引，但在我刚刚添加的 HASHBYTES 列上没有。每个表的唯一键也有聚集索引。

  1. 添加以检查更新的理想索引是什么？
  2. 我可以为每个表添加一个标准化索引吗？
  3. VARBINARY(MAX) 是正确的数据类型还是可以安全地将其缩小到更小的大小？

希望这足以让这个问题变得有意义。我需要尽快加快这个过程。

编辑：我正在添加一个大型 SQL 脚本作为示例，它具有表的 changeLog 版本和目标版本的示例表定义，以及为更新目标版本而运行的查询。

--OBJECT DEFINITIONS
CREATE TABLE [changeLog].[DimSalesOffice](
    [Sales Office Code] [varchar](3) NOT NULL,
    [CCN_Key] [uniqueidentifier] NOT NULL,
    [Sales Office Name (Short)] [nvarchar](14) NOT NULL,
    [Sales Office Name (Long)] [nvarchar](50) NOT NULL,
    [Sales Office City] [nvarchar](50) NOT NULL,
    [Sales Office StateProvince] [nvarchar](50) NOT NULL,
    [Sales Office Postal Code] [nvarchar](20) NOT NULL,
    [Sales Office Country Code] [varchar](3) NOT NULL,
    [Sales Office Address] [nvarchar](65) NOT NULL,
    [Sales Office Address (Line 2)] [nvarchar](65) NOT NULL,
    [Sales Office Name (Short - Native Language)] [nvarchar](14) NOT NULL,
    [Sales Office Name (Long - Native Language)] [nvarchar](50) NOT NULL,
    [Sales Office Address (Native Language)] [nvarchar](65) NOT NULL,
    [Sales Office Address (Line 2 - Native Language)] [nvarchar](65) NOT NULL,
    [Sales Office City (Native Language)] [nvarchar](100) NOT NULL,
    [Sales Office StateProvince (Native Language)] [nvarchar](100) NOT NULL,
    [Sales Office Region] [nvarchar](100) NULL,
    [Native Language Code] [varchar](2) NOT NULL
) ON [PRIMARY]
GO

CREATE TABLE [dbo].[DimSalesOffice](
    [SalesOffice_Key] [uniqueidentifier] NOT NULL,
    [Sales Office Code] [varchar](3) NOT NULL,
    [CCN_Key] [uniqueidentifier] NOT NULL,
    [Sales Office Name (Short)] [nvarchar](14) NOT NULL,
    [Sales Office Name (Long)] [nvarchar](50) NOT NULL,
    [Sales Office City] [nvarchar](50) NOT NULL,
    [Sales Office StateProvince] [nvarchar](50) NOT NULL,
    [Sales Office Postal Code] [nvarchar](20) NOT NULL,
    [Sales Office Country Code] [varchar](3) NOT NULL,
    [Sales Office Address] [nvarchar](65) NOT NULL,
    [Sales Office Address (Line 2)] [nvarchar](65) NOT NULL,
    [Sales Office Name (Short - Native Language)] [nvarchar](14) NOT NULL,
    [Sales Office Name (Long - Native Language)] [nvarchar](50) NOT NULL,
    [Sales Office Address (Native Language)] [nvarchar](65) NOT NULL,
    [Sales Office Address (Line 2 - Native Language)] [nvarchar](65) NOT NULL,
    [Sales Office City (Native Language)] [nvarchar](100) NOT NULL,
    [Sales Office StateProvince (Native Language)] [nvarchar](100) NOT NULL,
    [Sales Office Region] [nvarchar](100) NULL,
    [Native Language Code] [varchar](2) NOT NULL,
    [DW_CreatedOn] [datetime2](7) NULL,
    [DW_ModifiedOn] [datetime2](7) NULL,
    [DW_IsDeleted?] [bit] NULL,
    [DW_Checksum] [int] NULL,
    [Source_ModifiedOn] [datetime2](7) NULL,
    [DW_Hashbytes] [varbinary](max) NULL,
PRIMARY KEY NONCLUSTERED 
(
    [SalesOffice_Key] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO

ALTER TABLE [dbo].[DimSalesOffice] ADD  DEFAULT (newsequentialid()) FOR [SalesOffice_Key]
GO

CREATE UNIQUE CLUSTERED INDEX [IX_UK_DimSalesOffice] ON [dbo].[DimSalesOffice]
(
    [Sales Office Code] ASC
)
GO

--MERGE QUERY
DECLARE @InsertRecordCount INT, @UpdateRecordCount INT;

/*****UPDATE*****/
UPDATE [dbo].[DimSalesOffice] SET
    [CCN_Key] = [Source].[CCN_Key],
    [Sales Office Name (Short)] = [Source].[Sales Office Name (Short)],
    [Sales Office Name (Long)] = [Source].[Sales Office Name (Long)],
    [Sales Office City] = [Source].[Sales Office City],
    [Sales Office StateProvince] = [Source].[Sales Office StateProvince],
    [Sales Office Postal Code] = [Source].[Sales Office Postal Code],
    [Sales Office Country Code] = [Source].[Sales Office Country Code],
    [Sales Office Address] = [Source].[Sales Office Address],
    [Sales Office Address (Line 2)] = [Source].[Sales Office Address (Line 2)],
    [Sales Office Name (Short - Native Language)] = [Source].[Sales Office Name (Short - Native Language)],
    [Sales Office Name (Long - Native Language)] = [Source].[Sales Office Name (Long - Native Language)],
    [Sales Office Address (Native Language)] = [Source].[Sales Office Address (Native Language)],
    [Sales Office Address (Line 2 - Native Language)] = [Source].[Sales Office Address (Line 2 - Native Language)],
    [Sales Office City (Native Language)] = [Source].[Sales Office City (Native Language)],
    [Sales Office StateProvince (Native Language)] = [Source].[Sales Office StateProvince (Native Language)],
    [Sales Office Region] = [Source].[Sales Office Region],
    [Native Language Code] = [Source].[Native Language Code],
    [DW_Checksum] =
        CHECKSUM(
            [Source].[CCN_Key],
            [Source].[Sales Office Name (Short)],
            [Source].[Sales Office Name (Long)],
            [Source].[Sales Office City],
            [Source].[Sales Office StateProvince],
            [Source].[Sales Office Postal Code],
            [Source].[Sales Office Country Code],
            [Source].[Sales Office Address],
            [Source].[Sales Office Address (Line 2)],
            [Source].[Sales Office Name (Short - Native Language)],
            [Source].[Sales Office Name (Long - Native Language)],
            [Source].[Sales Office Address (Native Language)],
            [Source].[Sales Office Address (Line 2 - Native Language)],
            [Source].[Sales Office City (Native Language)],
            [Source].[Sales Office StateProvince (Native Language)],
            [Source].[Sales Office Region],
            [Source].[Native Language Code],
            0
        ),
    [DW_Hashbytes] = 
        HASHBYTES(
            'SHA2_256',
            ISNULL(CAST([Source].[CCN_Key] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Name (Short)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Name (Long)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office City] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office StateProvince] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Postal Code] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Country Code] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Address] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Address (Line 2)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Name (Short - Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Name (Long - Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Address (Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Address (Line 2 - Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office City (Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office StateProvince (Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Region] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Native Language Code] AS NVARCHAR(MAX)), '') + '|'
            + '0'
        ),
    [Source_ModifiedOn] = NULL,
    [DW_ModifiedOn] = GETUTCDATE(),
    [DW_IsDeleted?] = 0
FROM [changeLog].[DimSalesOffice] [Source]
JOIN [dbo].[DimSalesOffice]
    ON [Source].[Sales Office Code] = [DimSalesOffice].[Sales Office Code]
    AND ISNULL([DimSalesOffice].[DW_Hashbytes], HASHBYTES('SHA2_256', '')) <> HASHBYTES(
            'SHA2_256',
            ISNULL(CAST([Source].[CCN_Key] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Name (Short)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Name (Long)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office City] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office StateProvince] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Postal Code] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Country Code] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Address] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Address (Line 2)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Name (Short - Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Name (Long - Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Address (Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Address (Line 2 - Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office City (Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office StateProvince (Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Region] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Native Language Code] AS NVARCHAR(MAX)), '') + '|'
            + '0'
        )
SET @UpdateRecordCount = @@ROWCOUNT;

/*****Soft Deletes*****/
UPDATE [dbo].[DimSalesOffice] SET
    [DW_Checksum] = 0,
    [DW_Hashbytes] = 
        HASHBYTES(
            'SHA2_256',
            ISNULL(CAST([DimSalesOffice].[CCN_Key] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office Name (Short)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office Name (Long)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office City] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office StateProvince] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office Postal Code] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office Country Code] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office Address] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office Address (Line 2)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office Name (Short - Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office Name (Long - Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office Address (Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office Address (Line 2 - Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office City (Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office StateProvince (Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Sales Office Region] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([DimSalesOffice].[Native Language Code] AS NVARCHAR(MAX)), '') + '|'
            + '1'
        ),
    [Source_ModifiedOn] = NULL,
    [DW_ModifiedOn] = GETUTCDATE(),
    [DW_IsDeleted?] = 1
FROM [dbo].[DimSalesOffice]
WHERE NOT EXISTS
    (
        SELECT 1
        FROM [changeLog].[DimSalesOffice] [Source]
        WHERE [Source].[Sales Office Code] = [DimSalesOffice].[Sales Office Code]
    )
SET @UpdateRecordCount = @UpdateRecordCount + @@ROWCOUNT;

/*****INSERT*****/
INSERT INTO [dbo].[DimSalesOffice]
    (
        [Sales Office Code],
        [CCN_Key],
        [Sales Office Name (Short)],
        [Sales Office Name (Long)],
        [Sales Office City],
        [Sales Office StateProvince],
        [Sales Office Postal Code],
        [Sales Office Country Code],
        [Sales Office Address],
        [Sales Office Address (Line 2)],
        [Sales Office Name (Short - Native Language)],
        [Sales Office Name (Long - Native Language)],
        [Sales Office Address (Native Language)],
        [Sales Office Address (Line 2 - Native Language)],
        [Sales Office City (Native Language)],
        [Sales Office StateProvince (Native Language)],
        [Sales Office Region],
        [Native Language Code],
        [DW_Checksum],
        [DW_Hashbytes],
        [Source_ModifiedOn],
        [DW_ModifiedOn],
        [DW_IsDeleted?],
        [DW_CreatedOn]
    )
SELECT
    [Source].[Sales Office Code],
    [Source].[CCN_Key],
    [Source].[Sales Office Name (Short)],
    [Source].[Sales Office Name (Long)],
    [Source].[Sales Office City],
    [Source].[Sales Office StateProvince],
    [Source].[Sales Office Postal Code],
    [Source].[Sales Office Country Code],
    [Source].[Sales Office Address],
    [Source].[Sales Office Address (Line 2)],
    [Source].[Sales Office Name (Short - Native Language)],
    [Source].[Sales Office Name (Long - Native Language)],
    [Source].[Sales Office Address (Native Language)],
    [Source].[Sales Office Address (Line 2 - Native Language)],
    [Source].[Sales Office City (Native Language)],
    [Source].[Sales Office StateProvince (Native Language)],
    [Source].[Sales Office Region],
    [Source].[Native Language Code],
    [DW_Checksum] = 
        CHECKSUM(
            [Source].[CCN_Key],
            [Source].[Sales Office Name (Short)],
            [Source].[Sales Office Name (Long)],
            [Source].[Sales Office City],
            [Source].[Sales Office StateProvince],
            [Source].[Sales Office Postal Code],
            [Source].[Sales Office Country Code],
            [Source].[Sales Office Address],
            [Source].[Sales Office Address (Line 2)],
            [Source].[Sales Office Name (Short - Native Language)],
            [Source].[Sales Office Name (Long - Native Language)],
            [Source].[Sales Office Address (Native Language)],
            [Source].[Sales Office Address (Line 2 - Native Language)],
            [Source].[Sales Office City (Native Language)],
            [Source].[Sales Office StateProvince (Native Language)],
            [Source].[Sales Office Region],
            [Source].[Native Language Code],
            0
        ),
    [DW_Hashbytes] = 
        HASHBYTES(
            'SHA2_256',
            ISNULL(CAST([Source].[CCN_Key] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Name (Short)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Name (Long)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office City] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office StateProvince] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Postal Code] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Country Code] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Address] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Address (Line 2)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Name (Short - Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Name (Long - Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Address (Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Address (Line 2 - Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office City (Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office StateProvince (Native Language)] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Sales Office Region] AS NVARCHAR(MAX)), '') + '|'
            + ISNULL(CAST([Source].[Native Language Code] AS NVARCHAR(MAX)), '') + '|'
            + '0'
        ),
    [Source_ModifiedOn] = NULL,
    [DW_ModifiedOn] = GETUTCDATE(),
    [DW_IsDeleted?] = 0,
    [DW_CreatedOn] = GETUTCDATE()
FROM [changeLog].[DimSalesOffice] [Source]
WHERE NOT EXISTS
    (
        SELECT 1
        FROM [dbo].[DimSalesOffice]
        WHERE [Source].[Sales Office Code] = [DimSalesOffice].[Sales Office Code]
    )
SET @InsertRecordCount = @@ROWCOUNT;

SELECT [Update Record Count] = @UpdateRecordCount, [Insert Record Count] = @InsertRecordCount;
sql-server index-tuning

2 个回答

  1. HASHBYTES 的输出长度取决于所使用的算法。SHA2_256 产生 256 位或 32 字节。这是在文档中。将列声明binary(32)为很好。我目前使用的系统就是这样做的。

    • 1
  2. Best Answer

    反过来回答，因为它更具语言意义：

    1. VARBINARY(MAX) 是正确的数据类型还是可以安全地将其缩小到更小的大小？

    正如我在评论中提到的，SHA2_256 means它将输出哈希为 256 位，也就是 32 字节（1 字节中 8 位），这意味着VARBINARY您需要的最大大小是VARBINARY(32). 这在文档中提到HASBYTES()：

    输出符合算法标准：MD2、MD4、MD5为128位（16字节）；SHA 和 SHA1 为 160 位（20 字节）；SHA2_256 为 256 位（32 字节），SHA2_512 为512 位（64 字节）。

    所以，是的，你可以安全地将你的尺寸VARBINARY缩小到VARBINARY(32).

    1. 添加以检查更新的理想索引是什么？

    2. 我可以为每个表添加一个标准化索引吗？

    是的，在减少VARBINARY字段的大小后，可以将其添加到表的索引中。我会推荐一个非聚集索引，它以主键字段开头，然后HASHBYTES()在定义中将计算字段排在第二位。

    使其成为非聚集索引的原因是因为您通常希望避免索引中的热列，尤其是与每个非聚集索引一起存储的聚集索引。频繁更新的热列会导致对索引的大量写入，并且在聚集索引的情况下，这些写入也必须发生在每个非聚集索引上（因为聚集索引与它一起存储）。所有列上的行哈希肯定会经常更改。

    以主键字段开头是有意义的，因为您需要先按该字段连接以匹配相同的行，然后按HASHBYTES()计算字段连接以检查它们是否不同。

    您将如何改进哈希字节计算？我正在考虑索引一个计算列。

    是的，您可以使用计算列（甚至不需要持久化但可以）并对其进行索引，或者您也可以创建索引视图，我之前都做过。我会首先为计算列拍摄，因为它比索引视图更灵活一点，将实际行哈希耦合到表本身的行中，并且管理的对象更少。

    • 1

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