1. 什么是OB方案
OB（Offload/Backup）方案指的是将数据迁移到辅助存储设备以实现备份和卸载，从而优化主存储系统性能的方案。OB方案有着非常广泛的应用，尤其是在大数据量高并发的应用场景下。在SQL Server中，OB方案的主要应用是将历史数据或者低频访问数据迁移到归档库（Archive Database）或者中间层（Staging Layer）等存储设备中，从而将常用的数据集中在主数据库中，提高性能。
2. 存储过程实现OB方案
2.1 创建归档表
归档表是存储历史数据或者低频访问数据的表，一般来说它们与主数据库中的表结构相同。在创建归档表的时候，建议设置好索引以提高查询性能。以下是一个创建归档表的示例代码：
CREATE TABLE [ArchiveDB].[dbo].[SalesOrderArchive](
[SalesOrderID] [int] NOT NULL,
[RevisionNumber] [tinyint] NOT NULL,
[OrderDate] [datetime] NOT NULL,
[DueDate] [datetime] NOT NULL,
[ShipDate] [datetime] NULL,
[Status] [tinyint] NOT NULL,
[OnlineOrderFlag] [dbo].[Flag] NOT NULL,
[SalesOrderNumber] [dbo].[OrderNumber] NOT NULL,
[PurchaseOrderNumber] [dbo].[OrderNumber] NULL,
[AccountNumber] [dbo].[AccountNumber] NULL,
[CustomerID] [int] NOT NULL,
[SalesPersonID] [int] NULL,
[TerritoryID] [int] NULL,
[BillToAddressID] [int] NOT NULL,
[ShipToAddressID] [int] NOT NULL,
[ShipMethodID] [int] NOT NULL,
[CreditCardID] [int] NULL,
[CreditCardApprovalCode] [varchar](15) NULL,
[CurrencyRateID] [int] NULL,
[SubTotal] [money] NOT NULL,
[TaxAmt] [money] NOT NULL,
[Freight] [money] NOT NULL,
[TotalDue] AS ([SubTotal]+[TaxAmt]+[Freight]),
[Comment] [nvarchar](max) NULL,
[ModifiedDate] [datetime] NOT NULL DEFAULT (getdate()),
CONSTRAINT [PK_SalesOrderArchive_SalesOrderID_RevisionNumber] PRIMARY KEY CLUSTERED
(
[SalesOrderID] ASC,
[RevisionNumber] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY],
CONSTRAINT [AK_SalesOrderArchive_SalesOrderNumber_RevisionNumber] UNIQUE NONCLUSTERED
(
[SalesOrderNumber] ASC,
[RevisionNumber] 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]
2.2 编写存储过程
利用存储过程实现数据迁移的功能，存储过程中包括以下步骤：
定义临时表：将历史数据或者低频访问数据从主数据库中查询出来存储在临时表中
备份主数据库中的数据：在迁移前需要先备份主数据库中的数据以避免数据损失
将数据迁移至归档表中：将临时表中的历史数据或者低频访问数据迁移到归档表中
删除主数据库中的数据：将已经迁移到归档表中的数据从主数据库中删除以腾出空间
以下是一个利用存储过程实现OB方案的示例代码：
CREATE PROCEDURE [dbo].[ArchiveSalesOrder] (
@CurrentDate datetime
)
AS
BEGIN
SET NOCOUNT ON
-- Create a temporary table to hold the orders to be archived
CREATE TABLE #OrdersToBeArchived(
[SalesOrderID] [int] NOT NULL,
[RevisionNumber] [tinyint] NOT NULL,
[OrderDate] [datetime] NOT NULL,
[DueDate] [datetime] NOT NULL,
[ShipDate] [datetime] NULL,
[Status] [tinyint] NOT NULL,
[OnlineOrderFlag] [dbo].[Flag] NOT NULL,
[SalesOrderNumber] [dbo].[OrderNumber] NOT NULL,
[PurchaseOrderNumber] [dbo].[OrderNumber] NULL,
[AccountNumber] [dbo].[AccountNumber] NULL,
[CustomerID] [int] NOT NULL,
[SalesPersonID] [int] NULL,
[TerritoryID] [int] NULL,
[BillToAddressID] [int] NOT NULL,
[ShipToAddressID] [int] NOT NULL,
[ShipMethodID] [int] NOT NULL,
[CreditCardID] [int] NULL,
[CreditCardApprovalCode] [varchar](15) NULL,
[CurrencyRateID] [int] NULL,
[SubTotal] [money] NOT NULL,
[TaxAmt] [money] NOT NULL,
[Freight] [money] NOT NULL,
[TotalDue] AS ([SubTotal]+[TaxAmt]+[Freight]),
[Comment] [nvarchar](max) NULL,
[ModifiedDate] [datetime] NOT NULL
PRIMARY KEY CLUSTERED ([SalesOrderID] ASC, [RevisionNumber] ASC)
)
-- Backup current orders
BACKUP DATABASE [AdventureWorks2019] TO DISK = 'C:\Backup\AdventureWorks2019_' + CONVERT(varchar(8), @CurrentDate, 112) + '.bak'
-- Insert orders to be archived into the temporary table
INSERT INTO #OrdersToBeArchived (
[SalesOrderID],
[RevisionNumber],
[OrderDate],
[DueDate],
[ShipDate],
[Status],
[OnlineOrderFlag],
[SalesOrderNumber],
[PurchaseOrderNumber],
[AccountNumber],
[CustomerID],
[SalesPersonID],
[TerritoryID],
[BillToAddressID],
[ShipToAddressID],
[ShipMethodID],
[CreditCardID],
[CreditCardApprovalCode],
[CurrencyRateID],
[SubTotal],
[TaxAmt],
[Freight],
[Comment],
[ModifiedDate]
)
SELECT
[SalesOrderID],
[RevisionNumber],
[OrderDate],
[DueDate],
[ShipDate],
[Status],
[OnlineOrderFlag],
[SalesOrderNumber],
[PurchaseOrderNumber],
[AccountNumber],
[CustomerID],
[SalesPersonID],
[TerritoryID],
[BillToAddressID],
[ShipToAddressID],
[ShipMethodID],
[CreditCardID],
[CreditCardApprovalCode],
[CurrencyRateID],
[SubTotal],
[TaxAmt],
[Freight],
[Comment],
[ModifiedDate]
FROM [dbo].[SalesOrderHeader]
WHERE [ModifiedDate] < DATEADD(MONTH, -6, @CurrentDate)
-- Archive orders
INSERT INTO [ArchiveDB].[dbo].[SalesOrderArchive] (
[SalesOrderID],
[RevisionNumber],
[OrderDate],
[DueDate],
[ShipDate],
[Status],
[OnlineOrderFlag],
[SalesOrderNumber],
[PurchaseOrderNumber],
[AccountNumber],
[CustomerID],
[SalesPersonID],
[TerritoryID],
[BillToAddressID],
[ShipToAddressID],
[ShipMethodID],
[CreditCardID],
[CreditCardApprovalCode],
[CurrencyRateID],
[SubTotal],
[TaxAmt],
[Freight],
[Comment],
[ModifiedDate]
)
SELECT *
FROM #OrdersToBeArchived
-- Delete archived orders
DELETE [dbo].[SalesOrderHeader]
WHERE [SalesOrderID] IN (SELECT [SalesOrderID] FROM #OrdersToBeArchived)
DROP TABLE #OrdersToBeArchived
END
3. 注意事项
在应用OB方案的过程中需要注意以下事项：
备份：在数据迁移之前需要备份主数据库中的数据以避免数据损失，备份过程应该是非常及时和频繁的。
性能监控：为了确保系统性能，需要定期监视主数据库的性能指标，包括查询响应时间，CPU利用率，内存利用率等。
数据一致性：在迁移数据的过程中要确保数据的一致性，尤其是在高并发的场景下，需要避免数据重复、遗漏、或者损坏等情况。
迁移策略：根据业务需求和数据特征，制定合适的迁移策略，包括迁移频率，迁移粒度，迁移深度等。
4. 总结
OB方案是SQL Server中优秀的方案之一，它可以帮助开发人员将历史数据或者低频访问数据迁移到辅助存储设备中提高系统性能，同时也可以帮助节约数据库空间。在应用OB方案的过程中，需要注意备份、性能监控、数据一致性和迁移策略等方面，从而确保系统的可靠性和稳定性。