JTDS 和交易

Posted 2023-03-27

【中文标题】JTDS 和交易

【英文标题】：JTDS and Transactions

【发布时间】：2014-11-06 20:17:45

【问题描述】：

当我直接从 SSMS 调用存储过程 (MSSQL 2008R2) 或从 JTDS 调用它时，我会看到不同的行为。

首先，请看这两个程序。

CREATE PROCEDURE [Template].[UnguardedTest]
    @outparam_StartTransactionCount INT OUTPUT,
    @outparam_TransactionCount INT OUTPUT 

AS

BEGIN 

    SET NOCOUNT ON;
    SET XACT_ABORT ON;

    DECLARE @StartTranCount INT

    SELECT @StartTranCount = @@TRANCOUNT

    BEGIN TRANSACTION

    BEGIN
        SELECT @outparam_StartTransactionCount = @StartTranCount
        SELECT @outparam_TransactionCount = @@TRANCOUNT
    END

    COMMIT TRANSACTION

END 

第二个与第一个非常相似，除了它不会开始（或提交）事务，除非条目上的@@TRANCOUNT 为 0。

CREATE PROCEDURE [Template].[GuardedTest]
   @outparam_StartTransactionCount INT OUTPUT,
   @outparam_TransactionCount INT OUTPUT 

AS

BEGIN 

    SET NOCOUNT ON;
    SET XACT_ABORT ON;

    DECLARE @StartTranCount INT

    -- Record the @@TRANCOUNT at the beginning of this procedure / trigger.
    SELECT @StartTranCount = @@TRANCOUNT

    IF @StartTranCount = 0
        BEGIN TRANSACTION

    BEGIN
        SELECT @outparam_StartTransactionCount = @StartTranCount
        SELECT @outparam_TransactionCount = @@TRANCOUNT
    END

    IF @StartTranCount = 0
        COMMIT TRANSACTION

END 

如果我从 SSMS 调用它们，请使用以下代码

DECLARE @outparam_TransactionCount INT
DECLARE @outparam_StartTransactionCount INT

EXECUTE [Template].[UnguardedTest] @outparam_StartTransactionCount OUTPUT, @outparam_TransactionCount OUTPUT
SELECT 'UNGUARDED_NOT_WRAPPED' AS Description, @outparam_StartTransactionCount AS [StartTranCount],  @outparam_TransactionCount AS [TranCount]

BEGIN TRAN
    EXECUTE [Template].[UnguardedTest] @outparam_StartTransactionCount OUTPUT, @outparam_TransactionCount OUTPUT
    SELECT 'UNGUARDED_WRAPPED' AS Description, @outparam_StartTransactionCount AS [StartTranCount],  @outparam_TransactionCount AS [TranCount]
COMMIT TRAN

EXECUTE [Template].[GuardedTest] @outparam_StartTransactionCount OUTPUT, @outparam_TransactionCount OUTPUT
SELECT 'GUARDED_NOT_WRAPPED' AS Description, @outparam_StartTransactionCount AS [StartTranCount],  @outparam_TransactionCount AS [TranCount]

BEGIN TRAN
    EXECUTE [Template].[GuardedTest] @outparam_StartTransactionCount OUTPUT, @outparam_TransactionCount OUTPUT
    SELECT 'GUARDED_WRAPPED' AS Description, @outparam_StartTransactionCount AS [StartTranCount],  @outparam_TransactionCount AS [TranCount]
COMMIT TRAN

输出是我所期望的。

Description           StartTranCount TranCount
--------------------- -------------- -----------
UNGUARDED_NOT_WRAPPED 0              1

Description       StartTranCount TranCount
----------------- -------------- -----------
UNGUARDED_WRAPPED 1              2

Description         StartTranCount TranCount
------------------- -------------- -----------
GUARDED_NOT_WRAPPED 0              1

Description     StartTranCount TranCount
--------------- -------------- -----------
GUARDED_WRAPPED 1              1

即在事务中包装对过程的调用导致 StartTranCount 为 1，否则为零。

但是，当我通过 JTDS/JDBC 执行相同的过程时，按照下面的代码，我看到了奇怪的行为。

    int tc = -1, startTC = -1;

    final Connection con2 = DriverManager.getConnection(url);
    con2.setAutoCommit(false);
    final CallableStatement proc2 = con2.prepareCall(" call Template.GuardedTest(?,?) ");
    proc2.registerOutParameter("@outparam_StartTransactionCount", Types.INTEGER);
    proc2.registerOutParameter("@outparam_TransactionCount", Types.INTEGER);
    proc2.execute();
    startTC = proc2.getInt("@outparam_StartTransactionCount");
    tc = proc2.getInt("@outparam_TransactionCount");
    log.info("Guarded StartTC: " + startTC + ", TC: " + tc);
    proc2.close();          
    con2.commit();
    con2.close();

    final Connection con1 = DriverManager.getConnection(url);
    con1.setAutoCommit(false);
    final CallableStatement proc1 = con1.prepareCall(" call Template.UnguardedTest(?,?) ");
    proc1.registerOutParameter("@outparam_StartTransactionCount", Types.INTEGER);
    proc1.registerOutParameter("@outparam_TransactionCount", Types.INTEGER);
    proc1.execute();
    startTC = proc1.getInt("@outparam_StartTransactionCount");
    tc = proc1.getInt("@outparam_TransactionCount");
    log.info("Unguarded StartTC: " + startTC + ", TC: " + tc);
    proc1.close();
    con1.commit();
    con1.close();

我看到以下输出：

- Guarded StartTC: 0, TC: 2
- Unguarded StartTC: 0, TC: 2

正如我期望看到与上面的“包装”示例相同的值（据我所知，JDBC 在调用 setAutoCommit(false) 时会开始一个新事务，我真的不知道发生了什么。任何洞察力？

附加信息：

如果我切换到 Microsoft JDBC 驱动程序，我会得到预期的结果

MSFT Driver - Guarded StartTC: 1, TC: 1
MSFT Driver - Unguarded StartTC: 1, TC: 2

【参考方案1】：

我发现了这种行为的原因。

我假设 jTDS 在调用 setAutoCommit(false) 之后明确地开始了连接事务。事实上，它的行为并非如此。它所做的是在连接上发出SET IMPLICIT_TRANSACTIONS ON。

根据 Microsoft (http://msdn.microsoft.com/en-us/library/ms187807.aspx) - “当 IMPLICIT_TRANSACTIONS = ON 时，显式 BEGIN TRANSACTION 将启动两个嵌套事务。”

例如，如果我们在 SSMS 中执行以下操作

SET IMPLICIT_TRANSACTIONS ON
    EXECUTE [Template].[UnguardedTest] @outparam_StartTransactionCount OUTPUT, @outparam_TransactionCount OUTPUT
    SELECT 'UNGUARDED_IMPLICIT' AS Description, @outparam_StartTransactionCount AS [StartTranCount],  @outparam_TransactionCount AS [TranCount]
COMMIT TRAN

SET IMPLICIT_TRANSACTIONS ON
    EXECUTE [Template].[GuardedTest] @outparam_StartTransactionCount OUTPUT, @outparam_TransactionCount OUTPUT
    SELECT 'GUARDED_IMPLICIT' AS Description, @outparam_StartTransactionCount AS [StartTranCount],  @outparam_TransactionCount AS [TranCount]
COMMIT TRAN

我们得到以下信息：

Description        StartTranCount TranCount
------------------ -------------- -----------
UNGUARDED_IMPLICIT 0              2

Description      StartTranCount TranCount
---------------- -------------- -----------
GUARDED_IMPLICIT 0              2

这与我们在 jTDS 执行这些程序时得到的输出一致。