当oracle 12c获得行锁时，它会自动获得表锁吗？

Question

文档上说oracle12c，当一个行锁是aquired.That时需要一个表锁，这在sql server中是不是这样的，这是非常令人费解的。

A row lock, also called a TX lock, is a lock on a single row of a table. A transaction acquires a row lock for each row modified by one of the following statements: INSERT, UPDATE, DELETE, MERGE, and SELECT ... FOR UPDATE. The row lock exists until the transaction commits or rolls back.

***When a transaction obtains a row lock for a row, the transaction also acquires a table lock for the table in which the row resides***. The table lock prevents conflicting DDL operations that would override data changes in a current transaction.

有人能解释一下这一点吗？

Answer 1

发生的表锁是共享锁。同一个表上可以同时有任意数量的共享锁:它们不会相互干扰。

它们所做的就是阻止任何东西获取该表上的排它锁:比如说，改变表的结构。