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Enqueues are sophisticated locks for managing access to shared resources like tables, rows, jobs, and redo threads. An enqueue can be requested in different levels/mode: null, row share, row exclusive...

This event indicates the session is currently waiting on the Undo Segments and is often related to using system managed undo with an auto tuned undo retention period. In 10g, Oracle added the _undo_au...

SQL> select name from v$event_name where name like '%TX%'; NAME ---------------------------------------------------------------- enq: TX - row lock contention enq: TX - allocate ITL entry enq: TX -...

TT 队列锁在官方文档中介绍为TT, Temporary Table，但是实际在版本8i之后该队列锁更多参与在表空间管理事务中。 也可以称enqueue TT为tablespace lock。 作用 该enqueue TT队列锁用以在各种类型的表空间操作执行过程中避免出现死锁dead lock。 该enqueue lock的 ID2表明正在执行的操作种类，ID1表明该操作对应的表空间号V$Tabl...

介绍 TM enqueue ，这里的TM 是指Table Manipulation,最常见的enqueue 之一， enq: TM - contention 最常见的enqueue 并发争用等待之一。 使用 TM 锁在下列场景中被申请： 在OPS(早期的RAC)中LGWR会以ID1=0 & ID2=0去申请该队列锁来检查 DML_LOCKS 在所有实例中是全0还是全非0 当一...

New to Oracle 10g is the individual tracking of over 180 specific enqueues or internal Oracle locking mechanisms. One of these is the RO enqueue wait event for Object Reuse, and is used to synchronize...

Waits on High Water enqueue occur when allocating space beyond the high water mark of a segment during insert operations. Also, this wait occurs when reclaiming free space in lob segments after delete...

During Direct Path operations, the data is asynchronously written to the database files. At some stage the session needs to make sure that all outstanding asynchronous I/O have been completed to disk....

Direct path writes allow a session to queue an I/O write request and continue processing while the OS handles the I/O. If the session needs to know if an outstanding write is complete then it waits on...

Often related to sorting operations, check to see if occurring primarily in temp tablespaces. Solutions 1) Reading from temp tablespaces If the database parameter workarea_size_policy = AUTO: Increase...