cursor: mutex X等待事件

cursor: mutex * events等待事件用于Cursor Parent 和 Cursor stats类型的操作:

  • ‘cursor: mutex X’ , 某个进程申请以EXCL mode持有mutex时进入该等待, 该Mutex要么正被其他进程以SHRD模式参考,这导致X mode的申请必须要等待直到Ref count=0,  或者该mutex正被另一个进程以X mode持有。
  • 相关操作要求以EXCL X mode持有Mutex的:
    • 在一个父游标下创建一个新的子游标
    • 捕获SQL中的绑定变量
    • 更新或构件SQL统计信息V$SQLSTATS

 

详见 《深入理解Oracle中的Mutex》一文

 

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Cursor: Mutex X

  • Building a new cursor under a parent
    • Although this operation is cheaper, building many cursors under a parent cursor is not recommended.
  • Capture SQL bind data
  • Build or Update statistics blocks
  • Mutex is in the parent cursor.

A session waits on this event when it has requested a mutex for a cursor object in exclusive mode but must wait because it is busy. The mutex is busy because either the mutex is being held in exclusive mode by another session or the mutex is being held shared by one or more sessions. The existing mutex holder(s) must release the mutex before the mutex can be granted exclusively.

Solutions

Solutions for mutex wait problems are very similar to each other. See Analysis of Waits on Mutexes for more information and troubleshooting ideas.

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