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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   如果自己搞不定可以找诗檀软件专业ORACLE数据库优化团队成员帮您调优! 诗檀软件专业数据库优化团队 服务热线 ： 13764045638   QQ号:47079569    邮箱：[email protected]     Cursor: Mutex X Building a new cursor under a parent Although this operation is cheaper, building…

cursor: mutex * events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 S’ ， 某个进程以SHRD S mode申请一个Mutex， 而该Mutex要么被其他进程已EXCL X mode所持有，要么其他进程正在更新mutex 上的Ref Count。 相关类型的操作一般是检测父游标或者CURSOR统计信息数据， 此外查询V$SQLSTATS也会造成CURSOR statistics被查询   对父游标parent cursor的检测: 当找到一个游标并准备执行前需要对父游标进行检测。在这个对父游标的检测过程中要用到MUTEX:cursor: mutex S.。 当一个父游标下有很多个子游标时，则服务进程要遍历这些父游标下的子游标以便找到合适的子游标child cursor。 检测的mutex在parent cursor父游标中。 详见 《深入理解Oracle中的Mutex》一文   如果自己搞不定可以找诗檀软件专业ORACLE数据库优化团队成员帮您调优! 诗檀软件专业数据库优化团队 服务热线 ： 13764045638   QQ号:47079569    邮箱：[email protected]     Parent examination When finding a…

This is a read from a single copy of the control file. This happens in many cases. For example, while: Making a backup of the controlfiles Sharing information (between instances) from the controlfile Reading other blocks from the controlfiles Reading the header block Solutions Problem: If wait time is significant, it usually means there’s an…

This event occurs when a server process is updating all copies of the controlfile. Controlfile updates occur in the following situations: A checkpoint is reached The session starts a control file transaction (to make sure that the control files are up to date in case the session crashes before committing the control file transaction) The…

This is an Exadata wait event that occurs when a session is reading information from V$CELL, V$CELL_THREAD_HISTORY and other assocociated views/tables in this same category. Solutions This is not a very common wait event so contact Oracle Support if there are excessive waits on this event in your system.

cell smart table scan This is an Exadata wait event typically seen during full table scans that have been offloaded to the storage cells. This event replaces waits on “direct path read” in many cases. As with direct path reads, data is returned directly to the PGA rather than going through the buffer cache. When…

This is an Exadata wait event that occurs when doing a restore via RMAN. Exadata automatically offloads RMAN restore activities to the storage cells. Solutions Offloading the RMAN restore activity to the storage cells within an Exadata machine is probably a good thing, so there may no tuning required. If RMAN restores are affecting performance,…

This is an Exadata wait event that occurs when fast full index scans are offloaded to the storage cells. This event is related to cell smart table scan except that the object is an index. This event does not show up very frequently in Exadata probably because it is very good at performing full table…

This is an Exadata wait event that occurs when doing incremental level 1 backups via RMAN. Exadata automatically offloads RMAN backup activities to the storage cells. Solutions Offloading the RMAN backup activity to the storage cells within an Exadata machine is probably a good thing, so there may no tuning required. If RMAN backups are…

Sessions wait on this event in Exadata when creating tablespaces, adding files to an existing tablespace or automatic expansion a data file because of DML operations, e.g. data is being loaded into a table. One of the performance gains of Exadata when creating of modifying files is that activity is offloaded to the storage cells…