enq: AD - allocate AU

Synchronizes accesses to a specific OSM (Oracle Software Manager) disk AU

enq: AD - deallocate AU

Synchronizes accesses to a specific OSM disk AU

enq: AF - task serialization

Serializes access to an advisor task

enq: AG - contention

Synchronizes generation use of a particular workspace

enq: AO - contention

Synchronizes access to objects and scalar variables

enq: AS - contention

Synchronizes new service activation

enq: AT - contention

Serializes alter tablespace operations

enq: AW - AW$ table lock

Allows global access synchronization to the AW$ table (analytical workplace tables used in OLAP option)

enq: AW - AW generation lock

Gives in-use generation state for a particular workspace

enq: AW - user access for AW

Synchronizes user accesses to a particular workspace

enq: AW - AW state lock

Row lock synchronization for the AW$ table

enq: BR - file shrink

Lock held to prevent file from decreasing in physical size during RMAN backup

enq: BR - proxy-copy

Lock held to allow cleanup from backup mode during an RMAN proxy-copy backup

enq: CF - contention

Synchronizes accesses to the controlfile

enq: CI - contention

Coordinates cross-instance function invocations

enq: CL - drop label

Synchronizes accesses to label cache when dropping a label

enq: CL - compare labels

Synchronizes accesses to label cache for label comparison

enq: CM - gate

Serializes access to instance enqueue

enq: CM - instance

Indicates OSM disk group is mounted

enq: CT - global space management

Lock held during change tracking space management operations that affect the entire change tracking file

enq: CT - state

Lock held while enabling or disabling change tracking to ensure that it is enabled or disabled by only one user at a time

enq: CT - state change gate 2

Lock held while enabling or disabling change tracking in RAC

enq: CT - reading

Lock held to ensure that change tracking data remains in existence until a reader is done with it

enq: CT - CTWR process start/stop

Lock held to ensure that only one CTWR (Change Tracking Writer, which tracks block changes and is initiated by the alter database enable block change tracking command) process is started in a single instance

enq: CT - state change gate 1

Lock held while enabling or disabling change tracking in RAC

enq: CT - change stream ownership

Lock held by one instance while change tracking is enabled to guarantee access to thread-specific resources

enq: CT - local space management

Lock held during change tracking space management operations that affect just the data for one thread

enq: CU - contention

Recovers cursors in case of death while compiling

enq: DB - contention

Synchronizes modification of database wide supplemental logging attributes

enq: DD - contention

Synchronizes local accesses to ASM (Automatic Storage Management) disk groups

enq: DF - contention

Enqueue held by foreground or DBWR when a datafile is brought online in RAC

enq: DG - contention

Synchronizes accesses to ASM disk groups

enq: DL - contention

Lock to prevent index DDL during direct load

enq: DM - contention

Enqueue held by foreground or DBWR to synchronize database mount/open with other operations

enq: DN - contention

Serializes group number generations

enq: DP - contention

Synchronizes access to LDAP parameters

enq: DR - contention

Serializes the active distributed recovery operation

enq: DS - contention

Prevents a database suspend during LMON reconfiguration

enq: DT - contention

Serializes changing the default temporary table space and user creation

enq: DV - contention

Synchronizes access to lower-version Diana (PL/SQL intermediate representation)

enq: DX - contention

Serializes tightly coupled distributed transaction branches

enq: FA - access file

Synchronizes accesses to open ASM files

enq: FB - contention

Ensures that only one process can format data blocks in auto segment space managed tablespaces

enq: FC - open an ACD thread

LGWR opens an ACD thread

enq: FC - recover an ACD thread

SMON recovers an ACD thread

enq: FD - Marker generation

Synchronization

enq: FD - Flashback coordinator

Synchronization

enq: FD - Tablespace flashback on/off

Synchronization

enq: FD - Flashback on/off

Synchronization

enq: FG - serialize ACD relocate

Only 1 process in the cluster may do ACD relocation in a disk group

enq: FG - LGWR redo generation enq race

Resolves race condition to acquire Disk Group Redo Generation Enqueue

enq: FG - FG redo generation enq race

Resolves race condition to acquire Disk Group Redo Generation Enqueue

enq: FL - Flashback database log

Synchronizes access to Flashback database log

enq: FL - Flashback db command

Synchronizes Flashback Database and deletion of flashback logs

enq: FM - contention

Synchronizes access to global file mapping state

enq: FR - contention

Begins recovery of disk group

enq: FS - contention

Synchronizes recovery and file operations or synchronizes dictionary check

enq: FT - allow LGWR writes

Allows LGWR to generate redo in this thread

enq: FT - disable LGWR writes

Prevents LGWR from generating redo in this thread

enq: FU - contention

Serializes the capture of the DB feature, usage, and high watermark statistics

enq: HD - contention

Serializes accesses to ASM SGA data structures

enq: HP - contention

Synchronizes accesses to queue pages

enq: HQ - contention

Synchronizes the creation of new queue IDs

enq: HV - contention

Lock used to broker the high watermark during parallel inserts

enq: HW - contention

Lock used to broker the high watermark during parallel inserts

enq: IA - contention

Information not available

enq: ID - contention

Lock held to prevent other processes from performing controlfile transaction while NID is running

enq: IL - contention

Synchronizes accesses to internal label data structures

enq: IM - contention for blr

Serializes block recovery for IMU txn

enq: IR - contention

Synchronizes instance recovery

enq: IR - contention2

Synchronizes parallel instance recovery and shutdown immediate

enq: IS - contention

Synchronizes instance state changes

enq: IT - contention

Synchronizes accesses to a temp object's metadata

enq: JD - contention

Synchronizes dates between job queue coordinator and slave processes

enq: JI - contention

Lock held during materialized view operations (such as refresh, alter) to prevent concurrent operations on the same materialized view

enq: JQ - contention

Lock to prevent multiple instances from running a single job

enq: JS - contention

Synchronizes accesses to the job cache

enq: JS - coord post lock

Lock for coordinator posting

enq: JS - global wdw lock

Lock acquired when doing wdw ddl

enq: JS - job chain evaluate lock

Lock when job chain evaluated for steps to create

enq: JS - q mem clnup lck

Lock obtained when cleaning up q memory

enq: JS - slave enq get lock2

Gets run info locks before slv objget

enq: JS - slave enq get lock1

Slave locks exec pre to sess strt

enq: JS - running job cnt lock3

Lock to set running job count epost

enq: JS - running job cnt lock2

Lock to set running job count epre

enq: JS - running job cnt lock

Lock to get running job count

enq: JS - coord rcv lock

Lock when coord receives msg

enq: JS - queue lock

Lock on internal scheduler queue

enq: JS - job run lock - synchronize

Lock to prevent job from running elsewhere

enq: JS - job recov lock

Lock to recover jobs running on crashed RAC inst

enq: KK - context

Lock held by open redo thread, used by other instances to force a log switch

enq: KM - contention

Synchronizes various Resource Manager operations

enq: KP - contention

Synchronizes kupp process startup

enq: KT - contention

Synchronizes accesses to the current Resource Manager plan

enq: MD - contention

Lock held during materialized view log DDL statements

enq: MH - contention

Lock used for recovery when setting Mail Host for AQ e-mail notifications

enq: ML - contention

Lock used for recovery when setting Mail Port for AQ e-mail notifications

enq: MN - contention

Synchronizes updates to the LogMiner dictionary and prevents multiple instances from preparing the same LogMiner session

enq: MR - contention

Lock used to coordinate media recovery with other uses of datafiles

enq: MS - contention

Lock held during materialized view refresh to set up MV log

enq: MW - contention

Serializes the calibration of the manageability schedules with the Maintenance Window

enq: OC - contention

Synchronizes write accesses to the outline cache

enq: OL - contention

Synchronizes accesses to a particular outline name

enq: OQ - xsoqhiAlloc

Synchronizes access to olapi history allocation

enq: OQ - xsoqhiClose

Synchronizes access to olapi history closing

enq: OQ - xsoqhistrecb

Synchronizes access to olapi history globals

enq: OQ - xsoqhiFlush

Synchronizes access to olapi history flushing

enq: OQ - xsoq*histrecb

Synchronizes access to olapi history parameter CB

enq: PD - contention

Prevents others from updating the same property

enq: PE - contention

Synchronizes system parameter updates

enq: PF - contention

Synchronizes accesses to the password file

enq: PG - contention

Synchronizes global system parameter updates

enq: PH - contention

Lock used for recovery when setting proxy for AQ HTTP notifications

enq: PI - contention

Communicates remote Parallel Execution Server Process creation status

enq: PL - contention

Coordinates plug-in operation of transportable tablespaces

enq: PR - contention

Synchronizes process startup

enq: PS - contention

Parallel Execution Server Process reservation and synchronization

enq: PT - contention

Synchronizes access to ASM PST metadata

enq: PV - syncstart

Synchronizes slave start_shutdown

enq: PV - syncshut

Synchronizes instance shutdown_slvstart

enq: PW - prewarm status in dbw0

DBWR0 holds this enqueue indicating pre-warmed buffers present in cache

enq: PW - flush prewarm buffers

Direct Load needs to flush prewarmed buffers if DBWR0 holds this enqueue

enq: RB - contention

Serializes OSM rollback recovery operations

enq: RF - synch: per-SGA Broker metadata

Ensures r/w atomicity of DG configuration metadata per unique SGA

enq: RF - synchronization: critical ai

Synchronizes critical apply instance among primary instances

enq: RF - new AI

Synchronizes selection of the new apply instance

enq: RF - synchronization: chief

Anoints 1 instance's DMON (Data Guard Broker Monitor) as chief to other instance's DMONs

enq: RF - synchronization: HC master

Anoints 1 instance's DMON as health check master

enq: RF - synchronization: aifo master

Synchronizes critical apply instance failure detection and failover operation

enq: RF - atomicity

Ensures atomicity of log transport setup

enq: RN - contention

Coordinates nab computations of online logs during recovery

enq: RO - contention

Coordinates flushing of multiple objects

enq: RO - fast object reuse

Coordinates fast object reuse

enq: RP - contention

Enqueue held when resilvering is needed or when data block is repaired from mirror

enq: RS - file delete

Lock held to prevent file from accessing during space reclamation

enq: RS - persist alert level

Lock held to make alert level persistent

enq: RS - write alert level

Lock held to write alert level

enq: RS - read alert level

Lock held to read alert level

enq: RS - prevent aging list update

Lock held to prevent aging list update

enq: RS - record reuse

Lock held to prevent file from accessing while reusing circular record

enq: RS - prevent file delete

Lock held to prevent deleting file to reclaim space

enq: RT - contention

Thread locks held by LGWR, DBW0, and RVWR (Recovery Writer, used in Flashback Database operations) to indicate mounted or open status

enq: SB - contention

Synchronizes logical standby metadata operations

enq: SF - contention

Lock held for recovery when setting sender for AQ e-mail notifications

enq: SH - contention

Enqueue always acquired in no-wait mode; should seldom see this contention

enq: SI - contention

Prevents multiple streams table instantiations

enq: SK - contention

Serialize shrink of a segment

enq: SQ - contention

Lock to ensure that only one process can replenish the sequence cache

enq: SR - contention

Coordinates replication / streams operations

enq: SS - contention

Ensures that sort segments created during parallel DML operations aren't prematurely cleaned up

enq: ST - contention

Synchronizes space management activities in dictionary-managed tablespaces

enq: SU - contention

Serializes access to SaveUndo Segment

enq: SW - contention

Coordinates the 'alter system suspend' operation

enq: TA - contention

Serializes operations on undo segments and undo tablespaces

enq: TB - SQL Tuning Base Cache Update

Synchronizes writes to the SQL Tuning Base Existence Cache

enq: TB - SQL Tuning Base Cache Load

Synchronizes writes to the SQL Tuning Base Existence Cache

enq: TC - contention

Lock held to guarantee uniqueness of a tablespace checkpoint

enq: TC - contention2

Lock during setup of a unique tablespace checkpoint in null mode

enq: TD - KTF dump entries

KTF dumping time/scn mappings in SMON_SCN_TIME table

enq: TE - KTF broadcast

KTF broadcasting

enq: TF - contention

Serializes dropping of a temporary file

enq: TL - contention

Serializes threshold log table read and update

enq: TM - contention

Synchronizes accesses to an object

enq: TO - contention

Synchronizes DDL and DML operations on a temp object

enq: TQ - TM contention

TM access to the queue table

enq: TQ - DDL contention

DDL access to the queue table

enq: TQ - INI contention

TM access to the queue table

enq: TS - contention

Serializes accesses to temp segments

enq: TT - contention

Serializes DDL operations on tablespaces

enq: TW - contention

Lock held by one instance to wait for transactions on all instances to finish

enq: TX - contention

Lock held by a transaction to allow other transactions to wait for it

enq: TX - row lock contention

Lock held on a particular row by a transaction to prevent other transactions from modifying it

enq: TX - allocate ITL entry

Allocating an ITL entry in order to begin a transaction

enq: TX - index contention

Lock held on an index during a split to prevent other operations on it

enq: UL - contention

Lock held used by user applications

enq: US - contention

Lock held to perform DDL on the undo segment

enq: WA - contention

Lock used for recovery when setting watermark for memory usage in AQ notifications

enq: WF - contention

Enqueue used to serialize the flushing of snapshots

enq: WL - contention

Coordinates access to redo log files and archive logs

enq: WP - contention

Enqueue to handle concurrency between purging and baselines

enq: XH - contention

Lock used for recovery when setting No Proxy Domains for AQ HTTP notifications

enq: XR - quiesce database

Lock held during database quiesce

enq: XR - database force logging

Lock held during database force logging mode

enq: XY - contention

Lock used by Oracle Corporation for internal testing