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ORACLE等待事件:enq: TX

时间:2016-10-04 23:07  浏览:努力统计中...
enq: TX - row lock contention等待事件,这个是数据库里面一个比较常见的等待事件。enq是enqueue的缩写,它是一种保护共享资源的锁定机制,一个排队机制,先进先出(FIFO)。enq: TX - row lock co

enq: TX - row lock contention等待事件,这个是数据库里面一个比较常见的等待事件。enq是enqueue的缩写,它是一种保护共享资源的锁定机制,一个排队机制,先进先出(FIFO)。enq: TX - row lock contention等待事件,OACLE将其归类为application级别的等待事件。有些场景是因为应用逻辑设计不合理造成的。下面我们看看enq: TX - row lock contention的英文介绍:

This wait indicates time spent waiting for a TX lock, typically due to waiting to gain access to a row in a table that is currently locked by that transaction. The TX lock waited on is "TX-P2RAW-P3RAW" and the object / row that triggered the wait can usually be found in the ROW_WAIT_* columns of V$SESSION for the waiting session.

A TX lock is acquired when a transaction initiates its first change and is held until the transaction does a COMMIT or ROLLBACK. It is used mainly as a queuing mechanism so that other sessions can wait for the transaction to complete. The lock name (ID1 and ID2) of the TX lock reflect the transaction ID of the active transaction.

 

下面我们模拟一下enq: TX - row lock contention等待事件出现的场景,希望能对这个等待事件有较深的理解,主要参考了官方文档 ID 62354.1

1 Waits due to Row being locked by an active Transaction

这个是因为不同的session同时更新或删除同一个记录。例如,会话1持有row level lock,会话2在等待这个锁释放。准备测试环境和数据

SQL> create table test
  2  (  id number(10), 
  3     name varchar2(16)
  4  ) ;
 
Table created.
 
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