【Oracle等待事件】Transaction等待   注意如果 不当设置了例如10513 level 2的等待事件，那么可能造成该Transaction等待，原因是一些实例CRASH所产生的死事务，将不会被SMON主动回滚，这可能造成部分行数据始终被锁定 而不释放。   Definition:     Wait for a blocking transaction to be rolled back. Continue waiting until the transaction has been rolled back. Wait Time:      Wait for up to 1 second for a blocking transaction to be rolled back. Continue waiting until transaction has been rolled out. Parameters: P1 - Undo Segment No | Slot No within Undo header. P2 - Wrap Sequence [ max value is UB4MAXVAL ]. P3 - Count undo seg# SELECT * FROM v$rollstat WHERE usn = <undo seg#> slot#   This is the slot# within the transaction table that is being used to store a transaction. wrap#   Wrap or sequence number of the slot. For each new transaction this number increases. count   Number of times that Oracle7 has waited on this transaction. Commentary:     Used within kctwit() [ General TX wait routine . ] Once we have acquired the TX enqueue of the transaction we are waiting for , we must continue waiting until the blocking transaction has been committed/rolled back. If the transaction has been aborted, then we are waiting for PMON or SMON to complete the rollback (We may be waiting for SMON if a rollback segment needs recovery). This wait is interleaved with "undo segment recovery", because on each 'loop' we call ktucun(). Whether we see this event depends on the availability of the failed transactions enqueue. This wait may be more prevalent in a 2pc environment. Dependency:     We are dependent on the transaction being rolled out, but we could be waiting for either the local PMON, or a PMON from another instance [parallel server]. The Undo Segment No will tell us which instance we are waiting for , but at present this will remain an eyeball operation rather than automating it within ph2. Validity:    N/A Advise:         The waiting basically depends on the size of that transaction that is being rolled back. You may want to check if PMON / SMON is doing the rollback for a killed session and if so check Parameter:CLEANUP_ROLLBACK_ENTRIES. From 7.3 onwards View:X$KTUXE can be used to see the state of a transaction - it shows the transaction table entries in the rollback segment header. Related:        Lock:TX Note:34540.1 Enqueue Metrics. Bug:960962   Oracle8 OPS issue which can cause OPS deferred transaction recovery to take a long time, hence causing 'transaction' waits.