为什么 SELECT 查询不启动事务？ [甲骨文]

Question

我正在尝试调试下一个 oracle 过程：

create or replace PROCEDURE CASE_6_TRANS_2
AS
   V_NUM NUMBER(38,0);
BEGIN
  SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
  SELECT COUNT(AE.ID) INTO V_NUM FROM AUDIT_EVENT AE WHERE ID=10; 
  COMMIT; --BREAKPOINT
END CASE_6_TRANS_2;

但是当我想在断点处查看当前事务时，V$TRANSACTION table 是空的。

documentation 说：

A transaction begins when the first executable SQL statement is encountered. An executable SQL statement is a SQL statement that generates calls to a database instance, including DML and DDL statements and the SET TRANSACTION statement.

根据documentationSELECT查询是DML

交易是否开始但未显示在 V$TRANSACTION 中？
或者交易根本没有开始。为什么不呢？

Answer 1

事务以 SET TRANSACTION 开始，但是 transaction_id 的分配被延迟到第一个 DML（真正的 DML - 在我的经验中不是 SELECT 语句）

The same source says...

When a transaction begins, Oracle Database assigns the transaction to an available undo data segment to record the undo entries for the new transaction. A transaction ID is not allocated until an undo segment and transaction table slot are allocated, which occurs during the first DML statement.

这对我来说很有意义，没有理由提交或回滚 SELECT。

为什么 SELECT 查询不启动事务？ [甲骨文]

Why does not SELECT query start the transaction? [Oracle]

oracle

transactions