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:The CF enqueue is a Control File enqueue and happens during parallel access to the control files. The CF enqueue can be seen during any action that requires reading the control file, such as redo log archiving, redo log switches and begin backup commands
enq: CI - contention:The CI enqueue is the Cross Instance enqueue and happens when a session executes a cross instance call such as a query over a database link
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:This is the Format Block enqueue, used only when data blocks are using ASSM (Automatic Segment Space Management or bitmapped freelists). As we might expect, common FB enqueue relate to buffer busy conditions, especially since ASSM tends to cause performance problems under heavily DML loads
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:The HV enqueue is similar to the HW enqueue but for parallel direct path INSERTs
enq: HW - contention:The HW High Water enqueue occurs when competing processing are inserting into the same table and are trying to increase the high water mark of a table simultaneously. The HW enqueue can sometimes be removed by adding freelists or moving the segment to ASSM
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: KO - fast object checkpoint:The KO enqueue (a.k.a. enq: KO - fast object checkpoint) is seem in Oracle STAR transformations and high enqueue waits can indicate a sub-optimal DBWR background process
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:The PE enqueue is the Parameter Enqueue, which happens after “alter system” or “alter session” statements
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:The PS enqueue is the Parallel Slave synchronization enqueue which is only seen with Oracle parallel query. The PS enqueue happens when pre-processing problems occur when allocating the factotum (slave) processes for OPQ
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.The RO enqueue is the Reuse Object enqueue and is a cross-instance enqueue related to truncate table and drop table DDL operations
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:The SQ enqueue is the Sequence Cache enqueue is used to serialize access to Oracle sequences
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:The TC enqueue is related to the DBWR background process and occur when “alter tablespace” commands are issued. You will also see the TC enqueue when doing parallel full-table scans where rows are accessed directly, without being loaded into the data buffer cache
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:The TM enqueue related to Transaction Management and can be seen when tables are explicitly locked with reorganization activities that require locking of a table
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.these enqueues happen during disk sort operations
enq: TT - contention:The TT enqueue is used to avoid deadlocks in parallel tablespace operations. The TT enqueue can be seen with parallel create tablespace and parallel point in time recovery (PITR)
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:The UL enqueue is a User Lock enqueue and happens when a lock is requested in dbms_lock.request. The UL enqueue can be seen in Oracle Data Pump
enq: US - contention:The US enqueue happens with Oracle automatic UNDO management was undo segments are moved online and offline
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