Oracle 11g队列锁等待事件解释

短命女 2022-06-16 06:18 243阅读 0赞

有时候看到数据库报告中的enq:xxx不知道什么意思，现在列出来以供参考。

<table style="color:rgb(48,48,48); font-size:14px; line-height:20px"> 
 <tbody> 
 <tr> 
 <td>enq: AD – allocate AU</td> 
 <td>Synchronizes accesses to a specific OSM disk AU</td> 
 </tr> 
 <tr> 
 <td>enq: AD – deallocate AU</td> 
 <td>Synchronizes accesses to a specific OSM disk AU</td> 
 </tr> 
 <tr> 
 <td>enq: AF – task serialization</td> 
 <td>This enqueue is used to serialize access to an advisor task</td> 
 </tr> 
 <tr> 
 <td>enq: AG – contention</td> 
 <td>Synchronizes generation use of a particular workspace</td> 
 </tr> 
 <tr> 
 <td>enq: AO – contention</td> 
 <td>Synchronizes access to objects and scalar variables</td> 
 </tr> 
 <tr> 
 <td>enq: AS – contention</td> 
 <td>Synchronizes new service activation</td> 
 </tr> 
 <tr> 
 <td>enq: AT – contention</td> 
 <td>Serializes ‘alter tablespace’ operations</td> 
 </tr> 
 <tr> 
 <td>enq: AW – AW$ table lock</td> 
 <td>Global access synchronization to the AW$ table</td> 
 </tr> 
 <tr> 
 <td>enq: AW – AW generation lock</td> 
 <td>In-use generation state for a particular workspace</td> 
 </tr> 
 <tr> 
 <td>enq: AW – user access for AW</td> 
 <td>Synchronizes user accesses to a particular workspace</td> 
 </tr> 
 <tr> 
 <td>enq: AW – AW state lock</td> 
 <td>Row lock synchronization for the AW$ table</td> 
 </tr> 
 <tr> 
 <td>enq: BR – file shrink</td> 
 <td>Lock held to prevent file from decreasing in physical size during RMAN backup</td> 
 </tr> 
 <tr> 
 <td>enq: BR – proxy-copy</td> 
 <td>Lock held to allow cleanup from backup mode during an RMAN proxy-copy backup</td> 
 </tr> 
 <tr> 
 <td>enq: CF – contention</td> 
 <td>Synchronizes accesses to the controlfile</td> 
 </tr> 
 <tr> 
 <td>enq: CI – contention</td> 
 <td>Coordinates cross-instance function invocations</td> 
 </tr> 
 <tr> 
 <td>enq: CL – drop label</td> 
 <td>Synchronizes accesses to label cache when dropping a label</td> 
 </tr> 
 <tr> 
 <td>enq: CL – compare labels</td> 
 <td>Synchronizes accesses to label cache for label comparison</td> 
 </tr> 
 <tr> 
 <td>enq: CM – gate</td> 
 <td>Serialize access to instance enqueue</td> 
 </tr> 
 <tr> 
 <td>enq: CM – instance</td> 
 <td>Indicate OSM disk group is mounted</td> 
 </tr> 
 <tr> 
 <td>enq: CT – global space management</td> 
 <td>Lock held during change tracking space management operations that affect the entire change tracking file</td> 
 </tr> 
 <tr> 
 <td>enq: CT – state</td> 
 <td>Lock held while enabling or disabling change tracking, to ensure that it is only enabled or disabled by one user at a time</td> 
 </tr> 
 <tr> 
 <td>enq: CT – state change gate 2</td> 
 <td>Lock held while enabling or disabling change tracking in RAC</td> 
 </tr> 
 <tr> 
 <td>enq: CT – reading</td> 
 <td>Lock held to ensure that change tracking data remains in existence until a reader is done with it</td> 
 </tr> 
 <tr> 
 <td>enq: CT – CTWR process start/stop</td> 
 <td>Lock held to ensure that only one CTWR process is started in a single instance</td> 
 </tr> 
 <tr> 
 <td>enq: CT – state change gate 1</td> 
 <td>Lock held while enabling or disabling change tracking in RAC</td> 
 </tr> 
 <tr> 
 <td>enq: CT – change stream ownership</td> 
 <td>Lock held by one instance while change tracking is enabled, to guarantee access to thread-specific resources</td> 
 </tr> 
 <tr> 
 <td>enq: CT – local space management</td> 
 <td>Lock held during change tracking space management operations that affect just the data for one thread</td> 
 </tr> 
 <tr> 
 <td>enq: CU – contention</td> 
 <td>Recovers cursors in case of death while compiling</td> 
 </tr> 
 <tr> 
 <td>enq: DB – contention</td> 
 <td>Synchronizes modification of database wide supplemental logging attributes</td> 
 </tr> 
 <tr> 
 <td>enq: DD – contention</td> 
 <td>Synchronizes local accesses to ASM disk groups</td> 
 </tr> 
 <tr> 
 <td>enq: DF – contention</td> 
 <td>Enqueue held by foreground or DBWR when a datafile is brought online in RAC</td> 
 </tr> 
 <tr> 
 <td>enq: DG – contention</td> 
 <td>Synchronizes accesses to ASM disk groups</td> 
 </tr> 
 <tr> 
 <td>enq: DL – contention</td> 
 <td>Lock to prevent index DDL during direct load</td> 
 </tr> 
 <tr> 
 <td>enq: DM – contention</td> 
 <td>Enqueue held by foreground or DBWR to synchronize database mount/open with other operations</td> 
 </tr> 
 <tr> 
 <td>enq: DN – contention</td> 
 <td>Serializes group number generations</td> 
 </tr> 
 <tr> 
 <td>enq: DP – contention</td> 
 <td>Synchronizes access to LDAP parameters</td> 
 </tr> 
 <tr> 
 <td>enq: DR – contention</td> 
 <td>Serializes the active distributed recovery operation</td> 
 </tr> 
 <tr> 
 <td>enq: DS – contention</td> 
 <td>Prevents a database suspend during LMON reconfiguration</td> 
 </tr> 
 <tr> 
 <td>enq: DT – contention</td> 
 <td>Serializes changing the default temporary table space and user creation</td> 
 </tr> 
 <tr> 
 <td>enq: DV – contention</td> 
 <td>Synchronizes access to lower-version Diana (PL/SQL intermediate representation)</td> 
 </tr> 
 <tr> 
 <td>enq: DX – contention</td> 
 <td>Serializes tightly coupled distributed transaction branches</td> 
 </tr> 
 <tr> 
 <td>enq: FA – access file</td> 
 <td>Synchronizes accesses to open ASM files</td> 
 </tr> 
 <tr> 
 <td>enq: FB – contention</td> 
 <td>Ensures that only one process can format data blocks in auto segment space managed tablespaces</td> 
 </tr> 
 <tr> 
 <td>enq: FC – open an ACD thread</td> 
 <td>LGWR opens an ACD thread</td> 
 </tr> 
 <tr> 
 <td>enq: FC – recover an ACD thread</td> 
 <td>SMON recovers an ACD thread</td> 
 </tr> 
 <tr> 
 <td>enq: FD – Marker generation</td> 
 <td>Synchronization</td> 
 </tr> 
 <tr> 
 <td>enq: FD – Flashback coordinator</td> 
 <td>Synchronization</td> 
 </tr> 
 <tr> 
 <td>enq: FD – Tablespace flashback on/off</td> 
 <td>Synchronization</td> 
 </tr> 
 <tr> 
 <td>enq: FD – Flashback on/off</td> 
 <td>Synchronization</td> 
 </tr> 
 <tr> 
 <td>enq: FG – serialize ACD relocate</td> 
 <td>Only 1 process in the cluster may do ACD relocation in a disk group</td> 
 </tr> 
 <tr> 
 <td>enq: FG – LGWR redo generation enq race</td> 
 <td>Resolve race condition to acquire Disk Group Redo Generation Enqueue</td> 
 </tr> 
 <tr> 
 <td>enq: FG – FG redo generation enq race</td> 
 <td>Resolve race condition to acquire Disk Group Redo Generation Enqueue</td> 
 </tr> 
 <tr> 
 <td>enq: FL – Flashback database log</td> 
 <td>Synchronization</td> 
 </tr> 
 <tr> 
 <td>enq: FL – Flashback db command</td> 
 <td>Enqueue used to synchronize Flashback Database and deletion of flashback logs.</td> 
 </tr> 
 <tr> 
 <td>enq: FM – contention</td> 
 <td>Synchronizes access to global file mapping state</td> 
 </tr> 
 <tr> 
 <td>enq: FR – contention</td> 
 <td>Begin recovery of disk group</td> 
 </tr> 
 <tr> 
 <td>enq: FS – contention</td> 
 <td>Enqueue used to synchronize recovery and file operations or synchronize dictionary check</td> 
 </tr> 
 <tr> 
 <td>enq: FT – allow LGWR writes</td> 
 <td>Allow LGWR to generate redo in this thread</td> 
 </tr> 
 <tr> 
 <td>enq: FT – disable LGWR writes</td> 
 <td>Prevent LGWR from generating redo in this thread</td> 
 </tr> 
 <tr> 
 <td>enq: FU – contention</td> 
 <td>This enqueue is used to serialize the capture of the DB Feature, Usage and High Water Mark Statistics</td> 
 </tr> 
 <tr> 
 <td>enq: HD – contention</td> 
 <td>Serializes accesses to ASM SGA data structures</td> 
 </tr> 
 <tr> 
 <td>enq: HP – contention</td> 
 <td>Synchronizes accesses to queue pages</td> 
 </tr> 
 <tr> 
 <td>enq: HQ – contention</td> 
 <td>Synchronizes the creation of new queue IDs</td> 
 </tr> 
 <tr> 
 <td>enq: HV – contention</td> 
 <td>Lock used to broker the high water mark during parallel inserts</td> 
 </tr> 
 <tr> 
 <td>enq: HW – contention</td> 
 <td>Lock used to broker the high water mark during parallel inserts</td> 
 </tr> 
 <tr> 
 <td>enq: IA – contention</td> 
 </tr> 
 <tr> 
 <td>enq: ID – contention</td> 
 <td>Lock held to prevent other processes from performing controlfile transaction while NID is running</td> 
 </tr> 
 <tr> 
 <td>enq: IL – contention</td> 
 <td>Synchronizes accesses to internal label data structures</td> 
 </tr> 
 <tr> 
 <td>enq: IM – contention for blr</td> 
 <td>Serializes block recovery for IMU txn</td> 
 </tr> 
 <tr> 
 <td>enq: IR – contention</td> 
 <td>Synchronizes instance recovery</td> 
 </tr> 
 <tr> 
 <td>enq: IR – contention2</td> 
 <td>Synchronizes parallel instance recovery and shutdown immediate</td> 
 </tr> 
 <tr> 
 <td>enq: IS – contention</td> 
 <td>Enqueue used to synchronize instance state changes</td> 
 </tr> 
 <tr> 
 <td>enq: IT – contention</td> 
 <td>Synchronizes accesses to a temp object’s metadata</td> 
 </tr> 
 <tr> 
 <td>enq: JD – contention</td> 
 <td>Synchronizes dates between job queue coordinator and slave processes</td> 
 </tr> 
 <tr> 
 <td>enq: JI – contention</td> 
 <td>Lock held during materialized view operations (like refresh, alter) to prevent concurrent operations on the same materialized view</td> 
 </tr> 
 <tr> 
 <td>enq: JQ – contention</td> 
 <td>Lock to prevent multiple instances from running a single job</td> 
 </tr> 
 <tr> 
 <td>enq: JS – contention</td> 
 <td>Synchronizes accesses to the job cache</td> 
 </tr> 
 <tr> 
 <td>enq: JS – coord post lock</td> 
 <td>Lock for coordinator posting</td> 
 </tr> 
 <tr> 
 <td>enq: JS – global wdw lock</td> 
 <td>Lock acquired when doing wdw ddl</td> 
 </tr> 
 <tr> 
 <td>enq: JS – job chain evaluate lock</td> 
 <td>Lock when job chain evaluated for steps to create</td> 
 </tr> 
 <tr> 
 <td>enq: JS – q mem clnup lck</td> 
 <td>Lock obtained when cleaning up q memory</td> 
 </tr> 
 <tr> 
 <td>enq: JS – slave enq get lock2</td> 
 <td>Get run info locks before slv objget</td> 
 </tr> 
 <tr> 
 <td>enq: JS – slave enq get lock1</td> 
 <td>Slave locks exec pre to sess strt</td> 
 </tr> 
 <tr> 
 <td>enq: JS – running job cnt lock3</td> 
 <td>Lock to set running job count epost</td> 
 </tr> 
 <tr> 
 <td>enq: JS – running job cnt lock2</td> 
 <td>Lock to set running job count epre</td> 
 </tr> 
 <tr> 
 <td>enq: JS – running job cnt lock</td> 
 <td>Lock to get running job count</td> 
 </tr> 
 <tr> 
 <td>enq: JS – coord rcv lock</td> 
 <td>Lock when coord receives msg</td> 
 </tr> 
 <tr> 
 <td>enq: JS – queue lock</td> 
 <td>Lock on internal scheduler queue</td> 
 </tr> 
 <tr> 
 <td>enq: JS – job run lock – synchronize</td> 
 <td>Lock to prevent job from running elsewhere</td> 
 </tr> 
 <tr> 
 <td>enq: JS – job recov lock</td> 
 <td>Lock to recover jobs running on crashed RAC inst</td> 
 </tr> 
 <tr> 
 <td>enq: KK – context</td> 
 <td>Lock held by open redo thread, used by other instances to force a log switch</td> 
 </tr> 
 <tr> 
 <td>enq: KM – contention</td> 
 <td>Synchronizes various Resource Manager operations</td> 
 </tr> 
 <tr> 
 <td>enq: KP – contention</td> 
 <td>Synchronizes kupp process startup</td> 
 </tr> 
 <tr> 
 <td>enq: KT – contention</td> 
 <td>Synchronizes accesses to the current Resource Manager plan</td> 
 </tr> 
 <tr> 
 <td>enq: MD – contention</td> 
 <td>Lock held during materialized view log DDL statements</td> 
 </tr> 
 <tr> 
 <td>enq: MH – contention</td> 
 <td>Lock used for recovery when setting Mail Host for AQ e-mail notifications</td> 
 </tr> 
 <tr> 
 <td>enq: ML – contention</td> 
 <td>Lock used for recovery when setting Mail Port for AQ e-mail notifications</td> 
 </tr> 
 <tr> 
 <td>enq: MN – contention</td> 
 <td>Synchronizes updates to the LogMiner dictionary and prevents multiple instances from preparing the same LogMiner session</td> 
 </tr> 
 <tr> 
 <td>enq: MR – contention</td> 
 <td>Lock used to coordinate media recovery with other uses of datafiles</td> 
 </tr> 
 <tr> 
 <td>enq: MS – contention</td> 
 <td>Lock held during materialized view refresh to setup MV log</td> 
 </tr> 
 <tr> 
 <td>enq: MW – contention</td> 
 <td>This enqueue is used to serialize the calibration of the manageability schedules with the Maintenance Window</td> 
 </tr> 
 <tr> 
 <td>enq: OC – contention</td> 
 <td>Synchronizes write accesses to the outline cache</td> 
 </tr> 
 <tr> 
 <td>enq: OL – contention</td> 
 <td>Synchronizes accesses to a particular outline name</td> 
 </tr> 
 <tr> 
 <td>enq: OQ – xsoqhiAlloc</td> 
 <td>Synchronizes access to olapi history allocation</td> 
 </tr> 
 <tr> 
 <td>enq: OQ – xsoqhiClose</td> 
 <td>Synchronizes access to olapi history closing</td> 
 </tr> 
 <tr> 
 <td>enq: OQ – xsoqhistrecb</td> 
 <td>Synchronizes access to olapi history globals</td> 
 </tr> 
 <tr> 
 <td>enq: OQ – xsoqhiFlush</td> 
 <td>Synchronizes access to olapi history flushing</td> 
 </tr> 
 <tr> 
 <td>enq: OQ – xsoq*histrecb</td> 
 <td>Synchronizes access to olapi history parameter CB</td> 
 </tr> 
 <tr> 
 <td>enq: PD – contention</td> 
 <td>Prevents others from updating the same property</td> 
 </tr> 
 <tr> 
 <td>enq: PE – contention</td> 
 <td>Synchronizes system parameter updates</td> 
 </tr> 
 <tr> 
 <td>enq: PF – contention</td> 
 <td>Synchronizes accesses to the password file</td> 
 </tr> 
 <tr> 
 <td>enq: PG – contention</td> 
 <td>Synchronizes global system parameter updates</td> 
 </tr> 
 <tr> 
 <td>enq: PH – contention</td> 
 <td>Lock used for recovery when setting Proxy for AQ HTTP notifications</td> 
 </tr> 
 <tr> 
 <td>enq: PI – contention</td> 
 <td>Communicates remote Parallel Execution Server Process creation status</td> 
 </tr> 
 <tr> 
 <td>enq: PL – contention</td> 
 <td>Coordinates plug-in operation of transportable tablespaces</td> 
 </tr> 
 <tr> 
 <td>enq: PR – contention</td> 
 <td>Synchronizes process startup</td> 
 </tr> 
 <tr> 
 <td>enq: PS – contention</td> 
 <td>Parallel Execution Server Process reservation and synchronization</td> 
 </tr> 
 <tr> 
 <td>enq: PT – contention</td> 
 <td>Synchronizes access to ASM PST metadata</td> 
 </tr> 
 <tr> 
 <td>enq: PV – syncstart</td> 
 <td>Synchronizes slave start shutdown</td> 
 </tr> 
 <tr> 
 <td>enq: PV – syncshut</td> 
 <td>Synchronizes instance shutdown_slvstart</td> 
 </tr> 
 <tr> 
 <td>enq: PW – perwarm status in dbw0</td> 
 <td>DBWR 0 holds enqueue indicating prewarmed buffers present in cache</td> 
 </tr> 
 <tr> 
 <td>enq: PW – flush prewarm buffers</td> 
 <td>Direct Load needs to flush pre-warmed buffers if DBWR 0 holds enqueue</td> 
 </tr> 
 <tr> 
 <td>enq: RB – contention</td> 
 <td>Serializes OSM rollback recovery operations</td> 
 </tr> 
 <tr> 
 <td>enq: RF – synch: per-SGA Broker metadata</td> 
 <td>Ensures r/w atomicity of DG configuration metadata per unique SGA</td> 
 </tr> 
 <tr> 
 <td>enq: RF – synchronization: critical ai</td> 
 <td>Synchronizes critical apply instance among primary instances</td> 
 </tr> 
 <tr> 
 <td>enq: RF – new AI</td> 
 <td>Synchronizes selection of the new apply instance</td> 
 </tr> 
 <tr> 
 <td>enq: RF – synchronization: chief</td> 
 <td>Anoints 1 instance’s DMON as chief to other instances’ DMONs</td> 
 </tr> 
 <tr> 
 <td>enq: RF – synchronization: HC master</td> 
 <td>Anoints 1 instance’s DMON as health check master</td> 
 </tr> 
 <tr> 
 <td>enq: RF – synchronization: aifo master</td> 
 <td>Synchronizes apply instance failure detection and fail over operation</td> 
 </tr> 
 <tr> 
 <td>enq: RF – atomicity</td> 
 <td>Ensures atomicity of log transport setup</td> 
 </tr> 
 <tr> 
 <td>enq: RN – contention</td> 
 <td>Coordinates nab computations of online logs during recovery</td> 
 </tr> 
 <tr> 
 <td>enq: RO – contention</td> 
 <td>Coordinates flushing of multiple objects</td> 
 </tr> 
 <tr> 
 <td>enq: RO – fast object reuse</td> 
 <td>Coordinates fast object reuse</td> 
 </tr> 
 <tr> 
 <td>enq: RP – contention</td> 
 <td>Enqueue held when resilvering is needed or when data block is repaired from mirror</td> 
 </tr> 
 <tr> 
 <td>enq: RS – file delete</td> 
 <td>Lock held to prevent file from accessing during space reclamation</td> 
 </tr> 
 <tr> 
 <td>enq: RS – persist alert level</td> 
 <td>Lock held to make alert level persistent</td> 
 </tr> 
 <tr> 
 <td>enq: RS – write alert level</td> 
 <td>Lock held to write alert level</td> 
 </tr> 
 <tr> 
 <td>enq: RS – read alert level</td> 
 <td>Lock held to read alert level</td> 
 </tr> 
 <tr> 
 <td>enq: RS – prevent aging list update</td> 
 <td>Lock held to prevent aging list update</td> 
 </tr> 
 <tr> 
 <td>enq: RS – record reuse</td> 
 <td>Lock held to prevent file from accessing while reusing circular record</td> 
 </tr> 
 <tr> 
 <td>enq: RS – prevent file delete</td> 
 <td>Lock held to prevent deleting file to reclaim space</td> 
 </tr> 
 <tr> 
 <td>enq: RT – contention</td> 
 <td>Thread locks held by LGWR, DBW0, and RVWR to indicate mounted or open status</td> 
 </tr> 
 <tr> 
 <td>enq: SB – contention</td> 
 <td>Synchronizes Logical Standby metadata operations</td> 
 </tr> 
 <tr> 
 <td>enq: SF – contention</td> 
 <td>Lock used for recovery when setting Sender for AQ e-mail notifications</td> 
 </tr> 
 <tr> 
 <td>enq: SH – contention</td> 
 <td>Should seldom see this contention as this Enqueue is always acquired in no-wait mode</td> 
 </tr> 
 <tr> 
 <td>enq: SI – contention</td> 
 <td>Prevents multiple streams table instantiations</td> 
 </tr> 
 <tr> 
 <td>enq: SK – contention</td> 
 <td>Serialize shrink of a segment</td> 
 </tr> 
 <tr> 
 <td>enq: SQ – contention</td> 
 <td>Lock to ensure that only one process can replenish the sequence cache</td> 
 </tr> 
 <tr> 
 <td>enq: SR – contention</td> 
 <td>Coordinates replication / streams operations</td> 
 </tr> 
 <tr> 
 <td>enq: SS – contention</td> 
 <td>Ensures that sort segments created during parallel DML operations aren’t prematurely cleaned up</td> 
 </tr> 
 <tr> 
 <td>enq: ST – contention</td> 
 <td>Synchronizes space management activities in dictionary-managed tablespaces</td> 
 </tr> 
 <tr> 
 <td>enq: SU – contention</td> 
 <td>Serializes access to SaveUndo Segment</td> 
 </tr> 
 <tr> 
 <td>enq: SW – contention</td> 
 <td>Coordinates the ‘alter system suspend’ operation</td> 
 </tr> 
 <tr> 
 <td>enq: TA – contention</td> 
 <td>Serializes operations on undo segments and undo tablespaces</td> 
 </tr> 
 <tr> 
 <td>enq: TB – SQL Tuning Base Cache Update</td> 
 <td>Synchronizes writes to the SQL Tuning Base Existence Cache</td> 
 </tr> 
 <tr> 
 <td>enq: TB – SQL Tuning Base Cache Load</td> 
 <td>Synchronizes writes to the SQL Tuning Base Existence Cache</td> 
 </tr> 
 <tr> 
 <td>enq: TC – contention</td> 
 <td>Lock held to guarantee uniqueness of a tablespace checkpoint</td> 
 </tr> 
 <tr> 
 <td>enq: TC – contention2</td> 
 <td>Lock of setup of a unique tablespace checkpoint in null mode</td> 
 </tr> 
 <tr> 
 <td>enq: TD – KTF dump entries</td> 
 <td>KTF dumping time/scn mappings in SMON_SCN_TIME table</td> 
 </tr> 
 <tr> 
 <td>enq: TE – KTF broadcast</td> 
 <td>KTF broadcasting</td> 
 </tr> 
 <tr> 
 <td>enq: TF – contention</td> 
 <td>Serializes dropping of a temporary file</td> 
 </tr> 
 <tr> 
 <td>enq: TL – contention</td> 
 <td>Serializes threshold log table read and update</td> 
 </tr> 
 <tr> 
 <td>enq: TM – contention</td> 
 <td>Synchronizes accesses to an object</td> 
 </tr> 
 <tr> 
 <td>enq: TO – contention</td> 
 <td>Synchronizes DDL and DML operations on a temp object</td> 
 </tr> 
 <tr> 
 <td>enq: TQ – TM contention</td> 
 <td>TM access to the queue table</td> 
 </tr> 
 <tr> 
 <td>enq: TQ – DDL contention</td> 
 <td>TM access to the queue table</td> 
 </tr> 
 <tr> 
 <td>enq: TQ – INI contention</td> 
 <td>TM access to the queue table</td> 
 </tr> 
 <tr> 
 <td>enq: TS – contention</td> 
 <td>Serializes accesses to temp segments</td> 
 </tr> 
 <tr> 
 <td>enq: TT – contention</td> 
 <td>Serializes DDL operations on tablespaces</td> 
 </tr> 
 <tr> 
 <td>enq: TW – contention</td> 
 <td>Lock held by one instance to wait for transactions on all instances to finish</td> 
 </tr> 
 <tr> 
 <td>enq: TX – contention</td> 
 <td>Lock held by a transaction to allow other transactions to wait for it</td> 
 </tr> 
 <tr> 
 <td>enq: TX – row lock contention</td> 
 <td>Lock held on a particular row by a transaction to prevent other transactions from modifying it</td> 
 </tr> 
 <tr> 
 <td>enq: TX – allocate ITL entry</td> 
 <td>Allocating an ITL entry in order to begin a transaction</td> 
 </tr> 
 <tr> 
 <td>enq: TX – index contention</td> 
 <td>Lock held on an index during a split to prevent other operations on it</td> 
 </tr> 
 <tr> 
 <td>enq: UL – contention</td> 
 <td>Lock used by user applications</td> 
 </tr> 
 <tr> 
 <td>enq: US – contention</td> 
 <td>Lock held to perform DDL on the undo segment</td> 
 </tr> 
 <tr> 
 <td>enq: WA – contention</td> 
 <td>Lock used for recovery when setting Watermark for memory usage in AQ notifications</td> 
 </tr> 
 <tr> 
 <td>enq: WF – contention</td> 
 <td>This enqueue is used to serialize the flushing of snapshots</td> 
 </tr> 
 <tr> 
 <td>enq: WL – contention</td> 
 <td>Coordinates access to redo log files and archive logs</td> 
 </tr> 
 <tr> 
 <td>enq: WP – contention</td> 
 <td>This enqueue handles concurrency between purging and baselines</td> 
 </tr> 
 <tr> 
 <td>enq: XH – contention</td> 
 <td>Lock used for recovery when setting No Proxy Domains for AQ HTTP notifications</td> 
 </tr> 
 <tr> 
 <td>enq: XR – quiesce database</td> 
 <td>Lock held during database quiesce</td> 
 </tr> 
 <tr> 
 <td>enq: XR – database force logging</td> 
 <td>Lock held during database force logging mode</td> 
 </tr> 
 <tr> 
 <td>enq: XY – contention</td> 
 <td>Lock used for internal testing</td> 
 </tr> 
 </tbody> 
</table>

顶

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