Oracle 11g Enqueue Waits Desc
SELECT
eq_name "Enqueue",
ev.name "Enqueue Type",
eq.req_description "Description"
FROM v$enqueue_statistics eq, v$event_name ev
WHERE eq.event#=ev.event#
ORDER BY ev.name
Enqueue Enqueue Type Description
------------------------------ ---------------------------------------------------------------- --------------------------------------------------
Auto BMR enq: AB - ABMR process initialized Lock held to ensure that ABMR process is initializ
ed
Auto BMR enq: AB - ABMR process start/stop Lock held to ensure that only one ABMR is started
in the cluster
ASM Disk AU Lock enq: AD - allocate AU Synchronizes accesses to a specific ASM disk AU
ASM Disk AU Lock enq: AD - deallocate AU Synchronizes accesses to a specific ASM disk AU
ASM Disk AU Lock enq: AD - relocate AU Synchronizes accesses to a specific ASM disk AU
Edition Lock enq: AE - lock Prevent Dropping an edition in use
Advisor Framework enq: AF - task serialization This enqueue is used to serialize access to an adv
isor task
Analytic Workspace Generation enq: AG - contention Synchronizes generation use of a particular worksp
ace
ASM Enqueue enq: AM - ASM ACD Relocation Block ASM cache freeze
ASM Enqueue enq: AM - ASM Amdu Dump Allow only one AMDU dump when block read failure
ASM Enqueue enq: AM - ASM DD update SrRloc Serializes DD update for SrRloc
ASM Enqueue enq: AM - ASM File Destroy Prevent same file deletion race
ASM Enqueue enq: AM - ASM Grow ACD Serializes growing ASM ACD
ASM Enqueue enq: AM - ASM Password File Update Allow one ASM password file update per cluster at
a time
ASM Enqueue enq: AM - ASM User Prevents a user from being dropped if it owns any
open files
ASM Enqueue enq: AM - ASM cache freeze Start ASM cache freeze
ASM Enqueue enq: AM - ASM disk based alloc/dealloc Synchronizes disk based allocations/deallocations
ASM Enqueue enq: AM - ASM file descriptor Serializes access to ASM file descriptors
ASM Enqueue enq: AM - ASM file relocation Serializes file relocation shrink and drop
ASM Enqueue enq: AM - ASM reserved Check id1 of call for specific purpose
ASM Enqueue enq: AM - background COD reservation Reserve a background COD entry
ASM Enqueue enq: AM - block repair Serializes block repairs
ASM Enqueue enq: AM - client registration Registers DB instance to ASM client state object h
ash
ASM Enqueue enq: AM - disk offline Synchronizes disk offlines
ASM Enqueue enq: AM - group block ASM group block
ASM Enqueue enq: AM - group use Client group use
ASM Enqueue enq: AM - rollback COD reservation Reserve a rollback COD entry
ASM Enqueue enq: AM - shutdown Prevent DB instance registration during ASM instan
ce shutdown
MultiWriter Object Access enq: AO - contention Synchornizes access to objects and scalar variable
s
SPM Autopurge enq: AP - contention This enqueue is used to serialize the purging of S
QL plan baselines
Service Operations enq: AS - service activation Synchronizes new service activation
Alter Tablespace enq: AT - contention Serializes 'alter tablespace' operations
ASM volume locks enq: AV - AVD client registration Serialize inst reg and first DG use
ASM volume locks enq: AV - add/enable first volume in DG Serialize taking the AVD DG enqueue
ASM volume locks enq: AV - persistent DG number prevent DG number collisions
ASM volume locks enq: AV - volume relocate Serialize relocating volume extents
Analytic Workspace enq: AW - AW generation lock In-use generation state for a particular workspace
Analytic Workspace enq: AW - AW state lock Row lock synchronization for the AW$ table
Analytic Workspace enq: AW - AW$ table lock Global access synchronization to the AW$ table
Analytic Workspace enq: AW - user access for AW Synchronizes user accesses to a particular workspa
ce
KSXA Test Affinity Dictionary enq: AY - contention Affinity Dictionary test affinity synchronization
Global Transaction Branch enq: BB - 2PC across RAC instances 2PC distributed transaction branch across RAC inst
ances
BLOOM FILTER enq: BF - PMON Join Filter cleanup PMON bloom filter recovery
BLOOM FILTER enq: BF - allocation contention Allocate a bloom filter in a parallel statement
clonedb bitmap file access enq: BM - clonedb bitmap file write synchronizes clonedb bitmap file operations
Backup/Restore enq: BR - file shrink Lock held to prevent file from decreasing in physi
cal size during RMAN backup
Backup/Restore enq: BR - multi-section restore header Lock held to serialize file header access during m
ulti-section restore
Backup/Restore enq: BR - multi-section restore section Lock held to serialize section access during multi
-section restore
Backup/Restore enq: BR - perform autobackup Lock held to perform a new controlfile autobackup
Backup/Restore enq: BR - proxy-copy Lock held to allow cleanup from backup mode during
an RMAN proxy-copy backup
Backup/Restore enq: BR - request autobackup Lock held to request controlfile autobackups
Backup/Restore enq: BR - space info datafile hdr update Lock held to prevent multiple process to update th
e headers at the same time
Backup/Restore spare enq enq: BS - krb spare0 krb spare0
Backup/Restore spare enq enq: BS - krb spare1 krb spare1
Backup/Restore spare enq enq: BS - krb spare2 krb spare2
Backup/Restore spare enq enq: BS - krb spare3 krb spare3
Backup/Restore spare enq enq: BS - krb spare4 krb spare4
Backup/Restore spare enq enq: BS - krb spare5 krb spare5
Backup/Restore spare enq enq: BS - krb spare6 krb spare6
Backup/Restore spare enq enq: BS - krb spare7 krb spare7
Backup/Restore spare enq enq: BS - krb spare8 krb spare8
Backup/Restore spare enq enq: BS - krb spare9 krb spare9
Calibration enq: CA - contention Synchronizes various IO calibration runs
Controlfile Transaction enq: CF - contention Synchronizes accesses to the controlfile
Cross-Instance Call Invocation enq: CI - contention Coordinates cross-instance function invocations
Label Security cache enq: CL - compare labels Synchronizes accesses to label cache for label com
parison
Label Security cache enq: CL - drop label Synchronizes accesses to label cache when dropping
a label
ASM Instance Enqueue enq: CM - diskgroup dismount serialize asm diskgroup dismount
ASM Instance Enqueue enq: CM - gate serialize access to instance enqueue
ASM Instance Enqueue enq: CM - instance indicate ASM diskgroup is mounted
KTCN REG enq enq: CN - race with init during descriptor initialization
KTCN REG enq enq: CN - race with reg during transaction commit to see concurrent regist
rations
KTCN REG enq enq: CN - race with txn during registration
KTUCLO Master Slave enq enq: CO - master slave det enqueue held be Master in Cleanout Optim
Cleanup querycache registratio enq: CQ - contention Serializes access to cleanup client query cache re
ns gistrations
Reuse Block Range enq: CR - block range reuse ckpt Coordinates fast block range reuse ckpt
Block Change Tracking enq: CT - CTWR process start/stop Lock held to ensure that only one CTWR process is
started in a single instance
Block Change Tracking enq: CT - change stream ownership Lock held by one instance while change tracking is
enabled, to guarantee access to thread-specific r
esources
Block Change Tracking enq: CT - global space management Lock held during change tracking space management
operations that affect the entire change tracking
file
Block Change Tracking enq: CT - local space management Lock held during change tracking space management
operations that affect just the data for one threa
d
Block Change Tracking enq: CT - reading Lock held to ensure that change tracking data rema
ins in existence until a reader is done with it
Block Change Tracking enq: CT - state Lock held while enabling or disabling change track
ing, to ensure that it is only enabled or disabled
by one user at a time
Block Change Tracking enq: CT - state change gate 1 Lock held while enabling or disabling change track
ing in RAC
Block Change Tracking enq: CT - state change gate 2 Lock held while enabling or disabling change track
ing in RAC
Cursor enq: CU - contention Recovers cursors in case of death while compiling
TEXT: Index Specific Lock enq: CX - TEXT: Index Specific Lock Index Specific Lock on CTX index
DbsDriver enq: DB - contention Synchronizes modification of database wide supplem
entallogging attributes
ASM Local Disk Group enq: DD - contention Synchronizes local accesses to ASM disk groups
Datafile Online in RAC enq: DF - contention Enqueue held by foreground or DBWR when a datafile
is brought online in RAC
ASM Disk Group Modification enq: DG - contention Synchronizes accesses to ASM disk groups
Direct Loader Index Creation enq: DL - contention Lock to prevent index DDL during direct load
Database Mount/Open enq: DM - contention Enqueue held by foreground or DBWR to syncrhonize
database mount/open with other operations
Diskgroup number generator enq: DN - contention Serializes group number generations
ASM Disk Online Lock enq: DO - Staleness Registry create Synchronizes Staleness Registry creation
ASM Disk Online Lock enq: DO - disk online Synchronizes disk onlines and their recovery
ASM Disk Online Lock enq: DO - disk online operation Represents an active disk online operation
ASM Disk Online Lock enq: DO - disk online recovery Synchronizes disk onlines and their recovery
ASM Disk Online Lock enq: DO - startup of MARK process Synchronizes startup of MARK process
LDAP Parameter enq: DP - contention Synchronizes access to LDAP parameters
Distributed Recovery enq: DR - contention Serializes the active distributed recovery operati
on
Database Suspend enq: DS - contention Prevents a database suspend during LMON reconfigur
ation
Default Temporary Tablespace enq: DT - contention Serializes changing the default temporary table sp
aceand user creation
Diana Versioning enq: DV - contention Synchronizes access to lower-version Diana (PL/SQL
intermediate representation)
In memory Dispenser enq: DW - contention Serialize in memory dispenser operations
Distributed Transaction enq: DX - contention Serializes tightly coupled distributed transaction
branches
ASM File Access Lock enq: FA - access file Synchronizes accesses to open ASM files
Format Block enq: FB - contention Ensures that only one process can format data blco
ks in auto segment space managed tablespaces
Disk Group Chunk Mount enq: FC - open an ACD thread LGWR opens an ACD thread
Disk Group Chunk Mount enq: FC - recover an ACD thread SMON recovers an ACD thread
Flashback Database enq: FD - Flashback coordinator Synchronization
Flashback Database enq: FD - Flashback logical operations Synchronization
Flashback Database enq: FD - Flashback on/off Synchronization
Flashback Database enq: FD - Marker generation Synchronization
Flashback Database enq: FD - Restore point create/drop Synchronization
Flashback Database enq: FD - Tablespace flashback on/off Synchronization
KTFA Recovery enq: FE - contention Serializes flashback archive recovery
ACD Relocation Gate Enqueue enq: FG - FG redo generation enq race resolve race condition to acquire Disk Group Redo
Generation Enqueue
ACD Relocation Gate Enqueue enq: FG - LGWR redo generation enq race resolve race condition to acquire Disk Group Redo
Generation Enqueue
ACD Relocation Gate Enqueue enq: FG - serialize ACD relocate only 1 process in the cluster may do ACD relocatio
n in a disk group
Flashback database log enq: FL - Flashback database log Synchronization
Flashback database log enq: FL - Flashback db command Enqueue used to synchronize Flashback Database and
and deletion of flashback logs.
File Mapping enq: FM - contention Synchronizes access to global file mapping state
File Object enq: FP - global fob contention Synchronizes various File Object(FOB) operations
Disk Group Recovery enq: FR - contention begin recovery of disk group
Disk Group Recovery enq: FR - recover the thread wait for lock domain detach
Disk Group Recovery enq: FR - use the thread indicate this ACD thread is alive
File Set / Dictionary Check enq: FS - contention Enqueue used to synchronize recovery and file oper
ations or synchronize dictionary check
Disk Group Redo Generation enq: FT - allow LGWR writes allow LGWR to generate redo in this thread
Disk Group Redo Generation enq: FT - disable LGWR writes prevent LGWR from generating redo in this thread
DBFUS enq: FU - contention This enqueue is used to serialize the capture of t
he DB Feature Usage and High Water Mark
Statistics
ACD Xtnt Info CIC enq: FX - issue ACD Xtnt Relocation CIC ARB relocates ACD extent
ASM Disk Header enq: HD - contention Serializes accesses to ASM SGA data structures
Queue Page enq: HP - contention Synchronizes accesses to queue pages
Hash Queue enq: HQ - contention Synchronizes the creation of new queue IDs
Direct Loader High Water Mark enq: HV - contention Lock used to broker the high water mark during par
allel inserts
Segment High Water Mark enq: HW - contention Lock used to broker the high water mark during par
allel inserts
Internal enq: IA - contention
NID enq: ID - contention Lock held to prevent other processes from performi
ng controlfile transaction while NID is running
Label Security enq: IL - contention Synchronizes accesses to internal label data struc
tures
Kti blr lock enq: IM - contention for blr Serializes block recovery for IMU txn
Instance Recovery enq: IR - contention Synchronizes instance recovery
Instance Recovery enq: IR - contention2 Synchronizes parallel instance recovery and shutdo
wn immediate
Instance State enq: IS - contention Enqueue used to synchronize instance state changes
In-Mem Temp Table Meta Creatio enq: IT - contention Synchronizes accesses to a temp object's metadata
n
Job Queue Date enq: JD - contention Synchronizes dates between job queue coordinator a
nd slave processes
Materialized View enq: JI - contention Lock held during materialized view operations (lik
e refresh, alter) to prevent concurrent operations
on the same materialized view
Job Queue enq: JQ - contention Lock to prevent multiple instances from running a
single job
Job Scheduler enq: JS - aq sync Scheduler evt code and AQ sync
Job Scheduler enq: JS - contention Synchronizes accesses to the job cache
Job Scheduler enq: JS - evt notify Lock got during event notification
Job Scheduler enq: JS - evtsub add Lock got when adding subscriber to event q
Job Scheduler enq: JS - evtsub drop Lock got when dropping subscriber to event q
Job Scheduler enq: JS - job recov lock Lock to recover jobs running on crashed RAC inst
Job Scheduler enq: JS - job run lock - synchronize Lock to prevent job from running elsewhere
Job Scheduler enq: JS - q mem clnup lck Lock obtained when cleaning up q memory
Job Scheduler enq: JS - queue lock Lock on internal scheduler queue
Job Scheduler enq: JS - sch locl enqs Scheduler non-global enqueues
Job Scheduler enq: JS - wdw op Lock got when doing window open/close
SQL STATEMENT QUEUE enq: JX - SQL statement queue statement
SQL STATEMENT QUEUE enq: JX - cleanup of queue release SQL statement resources
Scheduler Master DBRM enq: KD - determine DBRM master Determine DBRM master
Scheduler enq: KM - contention Synchronizes various Resource Manager operations
Multiple Object Checkpoint enq: KO - fast object checkpoint Coordinates fast object checkpoint
Kupp Process Startup enq: KP - contention Synchronizes kupp process startup
ASM Attributes Enque enq: KQ - access ASM attribute Synchronization of ASM cached attributes
Scheduler Plan enq: KT - contention Synchronizes accesses to the current Resource Mana
ger plan
Materialized View Log DDL enq: MD - contention Lock held during materialized view log DDL stateme
nts
AQ Notification Mail Host enq: MH - contention Lock used for recovery when setting Mail Host for
AQ e-mail notifications
Master Key enq: MK - contention changing values in enc$
AQ Notification Mail Port enq: ML - contention Lock used for recovery when setting Mail Port for
AQ e-mail notifications
LogMiner enq: MN - contention Synchronizes updates to the LogMiner dictionary an
d prevents multiple instances from preparing the s
ame LogMiner session
MMON restricted session enq: MO - contention Serialize MMON operations for restricted sessions
Media Recovery enq: MR - contention Lock used to coordinate media recovery with other
uses of datafiles
Media Recovery enq: MR - datafile online Enqueue used to coordinate datafile offline in RAC
Media Recovery enq: MR - standby role transition Lock used to disallow concurrent standby role tran
sition attempt
Materialized View Refresh Log enq: MS - contention Lock held during materialized view refresh to setu
p MV log
Online Datafile Move enq: MV - datafile move Held during online datafile move operation or clea
nup
MWIN Schedule enq: MW - contention This enqueue is used to serialize the calibration
of the manageability schedules with the
Maintenance Window
ksz synch enq: MX - sync storage server info Lock held to generate a response to the storage se
rver information request when an instance is start
ing up
Outline Cache enq: OC - contention Synchronizes write accesses to the outline cache
Online DDLs enq: OD - Serializing DDLs Lock to prevent concurrent online DDLs
Outline Name enq: OL - contention Synchronizes accesses to a particular outline name
OLAPI Histories enq: OQ - xsoq*histrecb Synchronizes access to olapi history parameter CB
OLAPI Histories enq: OQ - xsoqhiAlloc Synchronizes access to olapi history allocation
OLAPI Histories enq: OQ - xsoqhiClose Synchronizes access to olapi history closing
OLAPI Histories enq: OQ - xsoqhiFlush Synchronizes access to olapi history flushing
OLAPI Histories enq: OQ - xsoqhistrecb Synchronizes access to olapi history globals
TEXT: Generic Lock enq: OT - TEXT: Generic Lock CTX Generic Locks
Encryption Wallet enq: OW - initialization initializing the wallet context
Encryption Wallet enq: OW - termination terminate the wallet context
Property Lock enq: PD - contention Prevents others from updating the same property
Parameter enq: PE - contention Synchronizes system parameter updates
Password File enq: PF - contention Synchronizes accesses to the password file
Global Parameter enq: PG - contention Synchronizes global system parameter updates
AQ Notification Proxy enq: PH - contention Lock used for recovery when setting Proxy for AQ H
TTP notifications
Remote PX Process Spawn Status enq: PI - contention Communicates remote Parallel Execution Server Proc
ess creation status
Transportable Tablespace enq: PL - contention Coordinates plug-in operation of transportable tab
lespaces
Process Startup enq: PR - contention Synchronizes process startup
PX Process Reservation enq: PS - contention Parallel Execution Server Process reservation and
synchronization
ASM Partnership and Status Tab enq: PT - contention Synchronizes access to ASM PST metadata
le
KSV slave startup enq: PV - syncshut Synchronizes instance shutdown_slvstart
KSV slave startup enq: PV - syncstart Synchronizes slave start_shutdown
Buffer Cache PreWarm enq: PW - flush prewarm buffers Direct Load needs to flush prewarmed buffers if DB
WR 0 holds enqueue
Buffer Cache PreWarm enq: PW - perwarm status in dbw0 DBWR 0 holds enqueue indicating prewarmed buffers
present in cache
ASM Rollback Recovery enq: RB - contention Serializes ASM rollback recovery operations
Result Cache: Enqueue enq: RC - Result Cache: Contention Coordinates access to a result-set
RAC Load enq: RD - RAC load update RAC load info
Block Repair/Resilvering enq: RE - block repair contention Synchronize block repair/resilvering operations
Data Guard Broker enq: RF - DG Broker Current File ID Identifies which configuration metadata file is cu
rrent
Data Guard Broker enq: RF - FSFO Observer Heartbeat Captures recent Fast-Start Failover Observer heart
beat information
Data Guard Broker enq: RF - FSFO Primary Shutdown suspended Records when FSFO Primary Shutdown is suspended
Data Guard Broker enq: RF - RF - Database Automatic Disable Means for detecting when database is being automat
ically disabled
Data Guard Broker enq: RF - atomicity Ensures atomicity of log transport setup
Data Guard Broker enq: RF - new AI Synchronizes selection of the new apply instance
Data Guard Broker enq: RF - synch: DG Broker metadata Ensures r/w atomicity of DG configuration metadata
Data Guard Broker enq: RF - synchronization: aifo master Synchronizes apply instance failure detection and
failover operation
Data Guard Broker enq: RF - synchronization: critical ai Synchronizes critical apply instance among primary
instances
wallet_set_mkey enq: RK - set key wallet master key rekey
RAC Encryption Wallet Lock enq: RL - RAC wallet lock RAC wallet lock
Redo Log Nab Computation enq: RN - contention Coordinates nab computations of online logs during
recovery
Multiple Object Reuse enq: RO - contention Coordinates flushing of multiple objects
Multiple Object Reuse enq: RO - fast object reuse Coordinates fast object reuse
Resilver / Repair enq: RP - contention Enqueue held when resilvering is needed or when da
tablock is repaired from mirror
Workload Capture and Replay enq: RR - contention Concurrent invocation of DBMS_WORKLOAD_* package A
PI
Reclaimable Space enq: RS - file delete Lock held to prevent file from accessing during sp
ace reclaimation
Reclaimable Space enq: RS - persist alert level Lock held to make alert level persistent
Reclaimable Space enq: RS - prevent aging list update Lock held to prevent aging list update
Reclaimable Space enq: RS - prevent file delete Lock held to prevent deleting file to reclaim spac
e
Reclaimable Space enq: RS - read alert level Lock held to read alert level
Reclaimable Space enq: RS - record reuse Lock held to prevent file from accessing while reu
sing circular record
Reclaimable Space enq: RS - write alert level Lock held to write alert level
Redo Thread enq: RT - contention Thread locks held by LGWR, DBW0, and RVWR to indic
ate mounted or open status
Redo Thread enq: RT - thread internal enable/disable Thread locks held by CKPT to synchronize thread en
able and disable
Rolling Migration enq: RU - contention Serializes rolling migration operations
Rolling Migration enq: RU - waiting Results of rolling migration CIC
Materialized View Flags enq: RW - MV metadata contention Lock held by CREATE/ALTER/DROP materialized viewwh
ile updating materialized view flags in detail tab
les
ASM Extent Relocation Lock enq: RX - relocate extent Synchronizes relocating ASM extents
ASM Extent Relocation Lock enq: RX - unlock extent Synchronizes unlocking ASM extents
LogicalStandby enq: SB - logical standby metadata Synchronizes Logical Standby metadata operations
LogicalStandby enq: SB - table instantiation Synchronizes table instantiation and EDS operation
s
Session Migration enq: SE - contention Synchronizes transparent session migration operati
ons
AQ Notification Sender enq: SF - contention Lock used for recovery when setting Sender for AQ
e-mail notifications
Active Session History Flushin enq: SH - contention Should seldom see this contention as this Enqueue
g is always acquired in no-wait mode
Streams Table Instantiation enq: SI - contention Prevents multiple streams tabel instantiations
KTSJ Slave Task Cancel enq: SJ - Slave Task Cancel Serializes cancelling task executed by slave proce
ss
Shrink Segment enq: SK - contention Serialize shrink of a segment
Serialize Lock request enq: SL - escalate lock sending lock escalate to LCK0
Serialize Lock request enq: SL - get lock sending lock req to LCK0
Serialize Lock request enq: SL - get lock for undo sending lock req for undo to LCK0
Shared Object enq: SO - contention Synchronizes access to Shared Object (PL/SQL Share
d Object Manager)
Spare Enqueue 0 enq: SP - contention 1 (1) due to one-off patch
Spare Enqueue 0 enq: SP - contention 2 (2) due to one-off patch
Spare Enqueue 0 enq: SP - contention 3 (3) due to one-off patch
Spare Enqueue 0 enq: SP - contention 4 (4) due to one-off patch
Sequence Cache enq: SQ - contention Lock to ensure that only one process can replenish
the sequence cache
Synchronized Replication enq: SR - contention Coordinates replication / streams operations
Sort Segment enq: SS - contention Ensures that sort segments created during parallel
DML operations aren't prematurely cleaned up
Space Transaction enq: ST - contention Synchronizes space management activities in dictio
nary-managed tablespaces
SaveUndo Segment enq: SU - contention Serializes access to SaveUndo Segment
Suspend Writes enq: SW - contention Coordinates the 'alter system suspend' operation
Spare Enqueue 1 enq: SX - contention 5 (5) due to one-off patch
Spare Enqueue 1 enq: SX - contention 6 (6) due to one-off patch
Instance Undo enq: TA - contention Serializes operations on undo segments and undo ta
blespaces
SQL Tuning Base Existence Cach enq: TB - SQL Tuning Base Cache Load Synchronizes writes to the SQL Tuning Base Existen
e ce Cache
SQL Tuning Base Existence Cach enq: TB - SQL Tuning Base Cache Update Synchronizes writes to the SQL Tuning Base Existen
e ce Cache
Tablespace Checkpoint enq: TC - contention Lock held to guarantee uniqueness of a tablespace
checkpoint
Tablespace Checkpoint enq: TC - contention2 Lock of setup of a unqiue tablespace checkpoint in
null mode
KTF map table enqueue enq: TD - KTF dump entries KTF dumping time/scn mappings in SMON_SCN_TIME tab
le
KTF broadcast enq: TE - KTF broadcast KTF broadcasting
Temporary File enq: TF - contention Serializes dropping of a temporary file
Threshold Chain enq: TH - metric threshold evaluation Serializes threshold in-memory chain access
Auto Task Serialization enq: TK - Auto Task Serialization Lock held by MMON to prevent other MMON spawning o
f Autotask Slave
Auto Task Serialization enq: TK - Auto Task Slave Lockout Serializes spawned Autotask Slaves
Log Lock enq: TL - contention Serializes threshold log table read and update
DML enq: TM - contention Synchronizes accesses to an object
Temp Object enq: TO - contention Synchronizes DDL and DML operations on a temp obje
ct
Runtime Fixed Table Purge enq: TP - contention Lock held during purge and dynamic reconfiguration
of fixed tables.
Queue table enqueue enq: TQ - DDL contention TM access to the queue table
Queue table enqueue enq: TQ - DDL-INI contention Streams DDL on queue table
Queue table enqueue enq: TQ - INI contention TM access to the queue table
Queue table enqueue enq: TQ - TM contention TM access to the queue table
Temporary Segment enq: TS - contention Serializes accesses to temp segments
Tablespace enq: TT - contention Serializes DDL operations on tablespaces
Cross-Instance Transaction enq: TW - contention Lock held by one instance to wait for transactions
on all instances to finish
Transaction enq: TX - allocate ITL entry Allocating an ITL entry in order to begin a transa
ction
Transaction enq: TX - contention Lock held by a transaction to allow other transact
ions to wait for it
Transaction enq: TX - index contention Lock held on an index during a split to prevent ot
her operations on it
Transaction enq: TX - row lock contention Lock held on a particular row by a transaction to
prevent other transactions from modifying it
User-defined enq: UL - contention Lock used by user applications
Undo Segment enq: US - contention Lock held to perform DDL on the undo segment
AQ Notification Watermark enq: WA - contention Lock used for recovery when setting Watermark for
memory usage in AQ notifications
AWR Flush enq: WF - contention This enqueue is used to serialize the flushing of
snapshots
Write gather local enqueue enq: WG - delete fso acquire lobid local enqueue when deleting fso
Write gather local enqueue enq: WG - lock fso acquire lobid local enqueue when locking fso
Being Written Redo Log enq: WL - RAC-wide SGA contention Serialize access to RAC-wide SGA
Being Written Redo Log enq: WL - RFS global state contention Serialize access to RFS global state
Being Written Redo Log enq: WL - Test access/locking Testing redo transport access/locking
Being Written Redo Log enq: WL - contention Coordinates access to redo log files and archive l
ogs
WLM Plan Operations enq: WM - WLM Plan activation Synchronizes new WLM Plan activation
AWR Purge enq: WP - contention This enqueue handles concurrency between purging a
nd baselines
LNS archiving log enq: WR - contention Coordinates access to logs by Async LNS and ARCH/F
G
XDB Configuration enq: XC - XDB Configuration Lock obtained when incrementing XDB configuration
version number
Auto Online Exadata disks enq: XD - ASM disk OFFLINE Serialize OFFLINE Exadata disk operations
Auto Online Exadata disks enq: XD - ASM disk ONLINE Serialize ONLINE Exadata disk operations
Auto Online Exadata disks enq: XD - ASM disk drop/add Serialize Auto Drop/Add Exadata disk operations
AQ Notification No-Proxy enq: XH - contention Lock used for recovery when setting No Proxy Domai
ns for AQ HTTP notifications
ASM Extent Fault Lock enq: XL - fault extent map Keep multiple processes from faulting in the same
extent chunk
ASM Extent Relocation Enqueue enq: XQ - purification wait for relocation before doing block purificatio
n
ASM Extent Relocation Enqueue enq: XQ - recovery prevent relocation during _recovery_asserts checki
ng
ASM Extent Relocation Enqueue enq: XQ - relocation wait for recovery before doing relocation
Quiesce / Force Logging enq: XR - database force logging Lock held during database force logging mode
Quiesce / Force Logging enq: XR - quiesce database Lock held during database quiesce
Internal Test enq: XY - contention Lock used for internal testing
Audit Partition enq: ZA - add std audit table partition lock held to add partition to std audit table
FGA Partition enq: ZF - add fga audit table partition lock held to add partition to fga audit table
File Group enq: ZG - contention Coordinates file group operations
Compression Analyzer enq: ZH - compression analysis Synchronizes analysis and insert into compression$
, prevents multiple threads analyzing the same tab
le during a load
repopulation file access enq: ZX - repopulation file write synchronizes file operations during repopulation
Global Context Action enq: ZZ - update hash tables lock held for updating global context hash tables
Enqueue Type Description
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
eq_name "Enqueue",
ev.name "Enqueue Type",
eq.req_description "Description"
FROM v$enqueue_statistics eq, v$event_name ev
WHERE eq.event#=ev.event#
ORDER BY ev.name
Enqueue Enqueue Type Description
------------------------------ ---------------------------------------------------------------- --------------------------------------------------
Auto BMR enq: AB - ABMR process initialized Lock held to ensure that ABMR process is initializ
ed
Auto BMR enq: AB - ABMR process start/stop Lock held to ensure that only one ABMR is started
in the cluster
ASM Disk AU Lock enq: AD - allocate AU Synchronizes accesses to a specific ASM disk AU
ASM Disk AU Lock enq: AD - deallocate AU Synchronizes accesses to a specific ASM disk AU
ASM Disk AU Lock enq: AD - relocate AU Synchronizes accesses to a specific ASM disk AU
Edition Lock enq: AE - lock Prevent Dropping an edition in use
Advisor Framework enq: AF - task serialization This enqueue is used to serialize access to an adv
isor task
Analytic Workspace Generation enq: AG - contention Synchronizes generation use of a particular worksp
ace
ASM Enqueue enq: AM - ASM ACD Relocation Block ASM cache freeze
ASM Enqueue enq: AM - ASM Amdu Dump Allow only one AMDU dump when block read failure
ASM Enqueue enq: AM - ASM DD update SrRloc Serializes DD update for SrRloc
ASM Enqueue enq: AM - ASM File Destroy Prevent same file deletion race
ASM Enqueue enq: AM - ASM Grow ACD Serializes growing ASM ACD
ASM Enqueue enq: AM - ASM Password File Update Allow one ASM password file update per cluster at
a time
ASM Enqueue enq: AM - ASM User Prevents a user from being dropped if it owns any
open files
ASM Enqueue enq: AM - ASM cache freeze Start ASM cache freeze
ASM Enqueue enq: AM - ASM disk based alloc/dealloc Synchronizes disk based allocations/deallocations
ASM Enqueue enq: AM - ASM file descriptor Serializes access to ASM file descriptors
ASM Enqueue enq: AM - ASM file relocation Serializes file relocation shrink and drop
ASM Enqueue enq: AM - ASM reserved Check id1 of call for specific purpose
ASM Enqueue enq: AM - background COD reservation Reserve a background COD entry
ASM Enqueue enq: AM - block repair Serializes block repairs
ASM Enqueue enq: AM - client registration Registers DB instance to ASM client state object h
ash
ASM Enqueue enq: AM - disk offline Synchronizes disk offlines
ASM Enqueue enq: AM - group block ASM group block
ASM Enqueue enq: AM - group use Client group use
ASM Enqueue enq: AM - rollback COD reservation Reserve a rollback COD entry
ASM Enqueue enq: AM - shutdown Prevent DB instance registration during ASM instan
ce shutdown
MultiWriter Object Access enq: AO - contention Synchornizes access to objects and scalar variable
s
SPM Autopurge enq: AP - contention This enqueue is used to serialize the purging of S
QL plan baselines
Service Operations enq: AS - service activation Synchronizes new service activation
Alter Tablespace enq: AT - contention Serializes 'alter tablespace' operations
ASM volume locks enq: AV - AVD client registration Serialize inst reg and first DG use
ASM volume locks enq: AV - add/enable first volume in DG Serialize taking the AVD DG enqueue
ASM volume locks enq: AV - persistent DG number prevent DG number collisions
ASM volume locks enq: AV - volume relocate Serialize relocating volume extents
Analytic Workspace enq: AW - AW generation lock In-use generation state for a particular workspace
Analytic Workspace enq: AW - AW state lock Row lock synchronization for the AW$ table
Analytic Workspace enq: AW - AW$ table lock Global access synchronization to the AW$ table
Analytic Workspace enq: AW - user access for AW Synchronizes user accesses to a particular workspa
ce
KSXA Test Affinity Dictionary enq: AY - contention Affinity Dictionary test affinity synchronization
Global Transaction Branch enq: BB - 2PC across RAC instances 2PC distributed transaction branch across RAC inst
ances
BLOOM FILTER enq: BF - PMON Join Filter cleanup PMON bloom filter recovery
BLOOM FILTER enq: BF - allocation contention Allocate a bloom filter in a parallel statement
clonedb bitmap file access enq: BM - clonedb bitmap file write synchronizes clonedb bitmap file operations
Backup/Restore enq: BR - file shrink Lock held to prevent file from decreasing in physi
cal size during RMAN backup
Backup/Restore enq: BR - multi-section restore header Lock held to serialize file header access during m
ulti-section restore
Backup/Restore enq: BR - multi-section restore section Lock held to serialize section access during multi
-section restore
Backup/Restore enq: BR - perform autobackup Lock held to perform a new controlfile autobackup
Backup/Restore enq: BR - proxy-copy Lock held to allow cleanup from backup mode during
an RMAN proxy-copy backup
Backup/Restore enq: BR - request autobackup Lock held to request controlfile autobackups
Backup/Restore enq: BR - space info datafile hdr update Lock held to prevent multiple process to update th
e headers at the same time
Backup/Restore spare enq enq: BS - krb spare0 krb spare0
Backup/Restore spare enq enq: BS - krb spare1 krb spare1
Backup/Restore spare enq enq: BS - krb spare2 krb spare2
Backup/Restore spare enq enq: BS - krb spare3 krb spare3
Backup/Restore spare enq enq: BS - krb spare4 krb spare4
Backup/Restore spare enq enq: BS - krb spare5 krb spare5
Backup/Restore spare enq enq: BS - krb spare6 krb spare6
Backup/Restore spare enq enq: BS - krb spare7 krb spare7
Backup/Restore spare enq enq: BS - krb spare8 krb spare8
Backup/Restore spare enq enq: BS - krb spare9 krb spare9
Calibration enq: CA - contention Synchronizes various IO calibration runs
Controlfile Transaction enq: CF - contention Synchronizes accesses to the controlfile
Cross-Instance Call Invocation enq: CI - contention Coordinates cross-instance function invocations
Label Security cache enq: CL - compare labels Synchronizes accesses to label cache for label com
parison
Label Security cache enq: CL - drop label Synchronizes accesses to label cache when dropping
a label
ASM Instance Enqueue enq: CM - diskgroup dismount serialize asm diskgroup dismount
ASM Instance Enqueue enq: CM - gate serialize access to instance enqueue
ASM Instance Enqueue enq: CM - instance indicate ASM diskgroup is mounted
KTCN REG enq enq: CN - race with init during descriptor initialization
KTCN REG enq enq: CN - race with reg during transaction commit to see concurrent regist
rations
KTCN REG enq enq: CN - race with txn during registration
KTUCLO Master Slave enq enq: CO - master slave det enqueue held be Master in Cleanout Optim
Cleanup querycache registratio enq: CQ - contention Serializes access to cleanup client query cache re
ns gistrations
Reuse Block Range enq: CR - block range reuse ckpt Coordinates fast block range reuse ckpt
Block Change Tracking enq: CT - CTWR process start/stop Lock held to ensure that only one CTWR process is
started in a single instance
Block Change Tracking enq: CT - change stream ownership Lock held by one instance while change tracking is
enabled, to guarantee access to thread-specific r
esources
Block Change Tracking enq: CT - global space management Lock held during change tracking space management
operations that affect the entire change tracking
file
Block Change Tracking enq: CT - local space management Lock held during change tracking space management
operations that affect just the data for one threa
d
Block Change Tracking enq: CT - reading Lock held to ensure that change tracking data rema
ins in existence until a reader is done with it
Block Change Tracking enq: CT - state Lock held while enabling or disabling change track
ing, to ensure that it is only enabled or disabled
by one user at a time
Block Change Tracking enq: CT - state change gate 1 Lock held while enabling or disabling change track
ing in RAC
Block Change Tracking enq: CT - state change gate 2 Lock held while enabling or disabling change track
ing in RAC
Cursor enq: CU - contention Recovers cursors in case of death while compiling
TEXT: Index Specific Lock enq: CX - TEXT: Index Specific Lock Index Specific Lock on CTX index
DbsDriver enq: DB - contention Synchronizes modification of database wide supplem
entallogging attributes
ASM Local Disk Group enq: DD - contention Synchronizes local accesses to ASM disk groups
Datafile Online in RAC enq: DF - contention Enqueue held by foreground or DBWR when a datafile
is brought online in RAC
ASM Disk Group Modification enq: DG - contention Synchronizes accesses to ASM disk groups
Direct Loader Index Creation enq: DL - contention Lock to prevent index DDL during direct load
Database Mount/Open enq: DM - contention Enqueue held by foreground or DBWR to syncrhonize
database mount/open with other operations
Diskgroup number generator enq: DN - contention Serializes group number generations
ASM Disk Online Lock enq: DO - Staleness Registry create Synchronizes Staleness Registry creation
ASM Disk Online Lock enq: DO - disk online Synchronizes disk onlines and their recovery
ASM Disk Online Lock enq: DO - disk online operation Represents an active disk online operation
ASM Disk Online Lock enq: DO - disk online recovery Synchronizes disk onlines and their recovery
ASM Disk Online Lock enq: DO - startup of MARK process Synchronizes startup of MARK process
LDAP Parameter enq: DP - contention Synchronizes access to LDAP parameters
Distributed Recovery enq: DR - contention Serializes the active distributed recovery operati
on
Database Suspend enq: DS - contention Prevents a database suspend during LMON reconfigur
ation
Default Temporary Tablespace enq: DT - contention Serializes changing the default temporary table sp
aceand user creation
Diana Versioning enq: DV - contention Synchronizes access to lower-version Diana (PL/SQL
intermediate representation)
In memory Dispenser enq: DW - contention Serialize in memory dispenser operations
Distributed Transaction enq: DX - contention Serializes tightly coupled distributed transaction
branches
ASM File Access Lock enq: FA - access file Synchronizes accesses to open ASM files
Format Block enq: FB - contention Ensures that only one process can format data blco
ks in auto segment space managed tablespaces
Disk Group Chunk Mount enq: FC - open an ACD thread LGWR opens an ACD thread
Disk Group Chunk Mount enq: FC - recover an ACD thread SMON recovers an ACD thread
Flashback Database enq: FD - Flashback coordinator Synchronization
Flashback Database enq: FD - Flashback logical operations Synchronization
Flashback Database enq: FD - Flashback on/off Synchronization
Flashback Database enq: FD - Marker generation Synchronization
Flashback Database enq: FD - Restore point create/drop Synchronization
Flashback Database enq: FD - Tablespace flashback on/off Synchronization
KTFA Recovery enq: FE - contention Serializes flashback archive recovery
ACD Relocation Gate Enqueue enq: FG - FG redo generation enq race resolve race condition to acquire Disk Group Redo
Generation Enqueue
ACD Relocation Gate Enqueue enq: FG - LGWR redo generation enq race resolve race condition to acquire Disk Group Redo
Generation Enqueue
ACD Relocation Gate Enqueue enq: FG - serialize ACD relocate only 1 process in the cluster may do ACD relocatio
n in a disk group
Flashback database log enq: FL - Flashback database log Synchronization
Flashback database log enq: FL - Flashback db command Enqueue used to synchronize Flashback Database and
and deletion of flashback logs.
File Mapping enq: FM - contention Synchronizes access to global file mapping state
File Object enq: FP - global fob contention Synchronizes various File Object(FOB) operations
Disk Group Recovery enq: FR - contention begin recovery of disk group
Disk Group Recovery enq: FR - recover the thread wait for lock domain detach
Disk Group Recovery enq: FR - use the thread indicate this ACD thread is alive
File Set / Dictionary Check enq: FS - contention Enqueue used to synchronize recovery and file oper
ations or synchronize dictionary check
Disk Group Redo Generation enq: FT - allow LGWR writes allow LGWR to generate redo in this thread
Disk Group Redo Generation enq: FT - disable LGWR writes prevent LGWR from generating redo in this thread
DBFUS enq: FU - contention This enqueue is used to serialize the capture of t
he DB Feature Usage and High Water Mark
Statistics
ACD Xtnt Info CIC enq: FX - issue ACD Xtnt Relocation CIC ARB relocates ACD extent
ASM Disk Header enq: HD - contention Serializes accesses to ASM SGA data structures
Queue Page enq: HP - contention Synchronizes accesses to queue pages
Hash Queue enq: HQ - contention Synchronizes the creation of new queue IDs
Direct Loader High Water Mark enq: HV - contention Lock used to broker the high water mark during par
allel inserts
Segment High Water Mark enq: HW - contention Lock used to broker the high water mark during par
allel inserts
Internal enq: IA - contention
NID enq: ID - contention Lock held to prevent other processes from performi
ng controlfile transaction while NID is running
Label Security enq: IL - contention Synchronizes accesses to internal label data struc
tures
Kti blr lock enq: IM - contention for blr Serializes block recovery for IMU txn
Instance Recovery enq: IR - contention Synchronizes instance recovery
Instance Recovery enq: IR - contention2 Synchronizes parallel instance recovery and shutdo
wn immediate
Instance State enq: IS - contention Enqueue used to synchronize instance state changes
In-Mem Temp Table Meta Creatio enq: IT - contention Synchronizes accesses to a temp object's metadata
n
Job Queue Date enq: JD - contention Synchronizes dates between job queue coordinator a
nd slave processes
Materialized View enq: JI - contention Lock held during materialized view operations (lik
e refresh, alter) to prevent concurrent operations
on the same materialized view
Job Queue enq: JQ - contention Lock to prevent multiple instances from running a
single job
Job Scheduler enq: JS - aq sync Scheduler evt code and AQ sync
Job Scheduler enq: JS - contention Synchronizes accesses to the job cache
Job Scheduler enq: JS - evt notify Lock got during event notification
Job Scheduler enq: JS - evtsub add Lock got when adding subscriber to event q
Job Scheduler enq: JS - evtsub drop Lock got when dropping subscriber to event q
Job Scheduler enq: JS - job recov lock Lock to recover jobs running on crashed RAC inst
Job Scheduler enq: JS - job run lock - synchronize Lock to prevent job from running elsewhere
Job Scheduler enq: JS - q mem clnup lck Lock obtained when cleaning up q memory
Job Scheduler enq: JS - queue lock Lock on internal scheduler queue
Job Scheduler enq: JS - sch locl enqs Scheduler non-global enqueues
Job Scheduler enq: JS - wdw op Lock got when doing window open/close
SQL STATEMENT QUEUE enq: JX - SQL statement queue statement
SQL STATEMENT QUEUE enq: JX - cleanup of queue release SQL statement resources
Scheduler Master DBRM enq: KD - determine DBRM master Determine DBRM master
Scheduler enq: KM - contention Synchronizes various Resource Manager operations
Multiple Object Checkpoint enq: KO - fast object checkpoint Coordinates fast object checkpoint
Kupp Process Startup enq: KP - contention Synchronizes kupp process startup
ASM Attributes Enque enq: KQ - access ASM attribute Synchronization of ASM cached attributes
Scheduler Plan enq: KT - contention Synchronizes accesses to the current Resource Mana
ger plan
Materialized View Log DDL enq: MD - contention Lock held during materialized view log DDL stateme
nts
AQ Notification Mail Host enq: MH - contention Lock used for recovery when setting Mail Host for
AQ e-mail notifications
Master Key enq: MK - contention changing values in enc$
AQ Notification Mail Port enq: ML - contention Lock used for recovery when setting Mail Port for
AQ e-mail notifications
LogMiner enq: MN - contention Synchronizes updates to the LogMiner dictionary an
d prevents multiple instances from preparing the s
ame LogMiner session
MMON restricted session enq: MO - contention Serialize MMON operations for restricted sessions
Media Recovery enq: MR - contention Lock used to coordinate media recovery with other
uses of datafiles
Media Recovery enq: MR - datafile online Enqueue used to coordinate datafile offline in RAC
Media Recovery enq: MR - standby role transition Lock used to disallow concurrent standby role tran
sition attempt
Materialized View Refresh Log enq: MS - contention Lock held during materialized view refresh to setu
p MV log
Online Datafile Move enq: MV - datafile move Held during online datafile move operation or clea
nup
MWIN Schedule enq: MW - contention This enqueue is used to serialize the calibration
of the manageability schedules with the
Maintenance Window
ksz synch enq: MX - sync storage server info Lock held to generate a response to the storage se
rver information request when an instance is start
ing up
Outline Cache enq: OC - contention Synchronizes write accesses to the outline cache
Online DDLs enq: OD - Serializing DDLs Lock to prevent concurrent online DDLs
Outline Name enq: OL - contention Synchronizes accesses to a particular outline name
OLAPI Histories enq: OQ - xsoq*histrecb Synchronizes access to olapi history parameter CB
OLAPI Histories enq: OQ - xsoqhiAlloc Synchronizes access to olapi history allocation
OLAPI Histories enq: OQ - xsoqhiClose Synchronizes access to olapi history closing
OLAPI Histories enq: OQ - xsoqhiFlush Synchronizes access to olapi history flushing
OLAPI Histories enq: OQ - xsoqhistrecb Synchronizes access to olapi history globals
TEXT: Generic Lock enq: OT - TEXT: Generic Lock CTX Generic Locks
Encryption Wallet enq: OW - initialization initializing the wallet context
Encryption Wallet enq: OW - termination terminate the wallet context
Property Lock enq: PD - contention Prevents others from updating the same property
Parameter enq: PE - contention Synchronizes system parameter updates
Password File enq: PF - contention Synchronizes accesses to the password file
Global Parameter enq: PG - contention Synchronizes global system parameter updates
AQ Notification Proxy enq: PH - contention Lock used for recovery when setting Proxy for AQ H
TTP notifications
Remote PX Process Spawn Status enq: PI - contention Communicates remote Parallel Execution Server Proc
ess creation status
Transportable Tablespace enq: PL - contention Coordinates plug-in operation of transportable tab
lespaces
Process Startup enq: PR - contention Synchronizes process startup
PX Process Reservation enq: PS - contention Parallel Execution Server Process reservation and
synchronization
ASM Partnership and Status Tab enq: PT - contention Synchronizes access to ASM PST metadata
le
KSV slave startup enq: PV - syncshut Synchronizes instance shutdown_slvstart
KSV slave startup enq: PV - syncstart Synchronizes slave start_shutdown
Buffer Cache PreWarm enq: PW - flush prewarm buffers Direct Load needs to flush prewarmed buffers if DB
WR 0 holds enqueue
Buffer Cache PreWarm enq: PW - perwarm status in dbw0 DBWR 0 holds enqueue indicating prewarmed buffers
present in cache
ASM Rollback Recovery enq: RB - contention Serializes ASM rollback recovery operations
Result Cache: Enqueue enq: RC - Result Cache: Contention Coordinates access to a result-set
RAC Load enq: RD - RAC load update RAC load info
Block Repair/Resilvering enq: RE - block repair contention Synchronize block repair/resilvering operations
Data Guard Broker enq: RF - DG Broker Current File ID Identifies which configuration metadata file is cu
rrent
Data Guard Broker enq: RF - FSFO Observer Heartbeat Captures recent Fast-Start Failover Observer heart
beat information
Data Guard Broker enq: RF - FSFO Primary Shutdown suspended Records when FSFO Primary Shutdown is suspended
Data Guard Broker enq: RF - RF - Database Automatic Disable Means for detecting when database is being automat
ically disabled
Data Guard Broker enq: RF - atomicity Ensures atomicity of log transport setup
Data Guard Broker enq: RF - new AI Synchronizes selection of the new apply instance
Data Guard Broker enq: RF - synch: DG Broker metadata Ensures r/w atomicity of DG configuration metadata
Data Guard Broker enq: RF - synchronization: aifo master Synchronizes apply instance failure detection and
failover operation
Data Guard Broker enq: RF - synchronization: critical ai Synchronizes critical apply instance among primary
instances
wallet_set_mkey enq: RK - set key wallet master key rekey
RAC Encryption Wallet Lock enq: RL - RAC wallet lock RAC wallet lock
Redo Log Nab Computation enq: RN - contention Coordinates nab computations of online logs during
recovery
Multiple Object Reuse enq: RO - contention Coordinates flushing of multiple objects
Multiple Object Reuse enq: RO - fast object reuse Coordinates fast object reuse
Resilver / Repair enq: RP - contention Enqueue held when resilvering is needed or when da
tablock is repaired from mirror
Workload Capture and Replay enq: RR - contention Concurrent invocation of DBMS_WORKLOAD_* package A
PI
Reclaimable Space enq: RS - file delete Lock held to prevent file from accessing during sp
ace reclaimation
Reclaimable Space enq: RS - persist alert level Lock held to make alert level persistent
Reclaimable Space enq: RS - prevent aging list update Lock held to prevent aging list update
Reclaimable Space enq: RS - prevent file delete Lock held to prevent deleting file to reclaim spac
e
Reclaimable Space enq: RS - read alert level Lock held to read alert level
Reclaimable Space enq: RS - record reuse Lock held to prevent file from accessing while reu
sing circular record
Reclaimable Space enq: RS - write alert level Lock held to write alert level
Redo Thread enq: RT - contention Thread locks held by LGWR, DBW0, and RVWR to indic
ate mounted or open status
Redo Thread enq: RT - thread internal enable/disable Thread locks held by CKPT to synchronize thread en
able and disable
Rolling Migration enq: RU - contention Serializes rolling migration operations
Rolling Migration enq: RU - waiting Results of rolling migration CIC
Materialized View Flags enq: RW - MV metadata contention Lock held by CREATE/ALTER/DROP materialized viewwh
ile updating materialized view flags in detail tab
les
ASM Extent Relocation Lock enq: RX - relocate extent Synchronizes relocating ASM extents
ASM Extent Relocation Lock enq: RX - unlock extent Synchronizes unlocking ASM extents
LogicalStandby enq: SB - logical standby metadata Synchronizes Logical Standby metadata operations
LogicalStandby enq: SB - table instantiation Synchronizes table instantiation and EDS operation
s
Session Migration enq: SE - contention Synchronizes transparent session migration operati
ons
AQ Notification Sender enq: SF - contention Lock used for recovery when setting Sender for AQ
e-mail notifications
Active Session History Flushin enq: SH - contention Should seldom see this contention as this Enqueue
g is always acquired in no-wait mode
Streams Table Instantiation enq: SI - contention Prevents multiple streams tabel instantiations
KTSJ Slave Task Cancel enq: SJ - Slave Task Cancel Serializes cancelling task executed by slave proce
ss
Shrink Segment enq: SK - contention Serialize shrink of a segment
Serialize Lock request enq: SL - escalate lock sending lock escalate to LCK0
Serialize Lock request enq: SL - get lock sending lock req to LCK0
Serialize Lock request enq: SL - get lock for undo sending lock req for undo to LCK0
Shared Object enq: SO - contention Synchronizes access to Shared Object (PL/SQL Share
d Object Manager)
Spare Enqueue 0 enq: SP - contention 1 (1) due to one-off patch
Spare Enqueue 0 enq: SP - contention 2 (2) due to one-off patch
Spare Enqueue 0 enq: SP - contention 3 (3) due to one-off patch
Spare Enqueue 0 enq: SP - contention 4 (4) due to one-off patch
Sequence Cache enq: SQ - contention Lock to ensure that only one process can replenish
the sequence cache
Synchronized Replication enq: SR - contention Coordinates replication / streams operations
Sort Segment enq: SS - contention Ensures that sort segments created during parallel
DML operations aren't prematurely cleaned up
Space Transaction enq: ST - contention Synchronizes space management activities in dictio
nary-managed tablespaces
SaveUndo Segment enq: SU - contention Serializes access to SaveUndo Segment
Suspend Writes enq: SW - contention Coordinates the 'alter system suspend' operation
Spare Enqueue 1 enq: SX - contention 5 (5) due to one-off patch
Spare Enqueue 1 enq: SX - contention 6 (6) due to one-off patch
Instance Undo enq: TA - contention Serializes operations on undo segments and undo ta
blespaces
SQL Tuning Base Existence Cach enq: TB - SQL Tuning Base Cache Load Synchronizes writes to the SQL Tuning Base Existen
e ce Cache
SQL Tuning Base Existence Cach enq: TB - SQL Tuning Base Cache Update Synchronizes writes to the SQL Tuning Base Existen
e ce Cache
Tablespace Checkpoint enq: TC - contention Lock held to guarantee uniqueness of a tablespace
checkpoint
Tablespace Checkpoint enq: TC - contention2 Lock of setup of a unqiue tablespace checkpoint in
null mode
KTF map table enqueue enq: TD - KTF dump entries KTF dumping time/scn mappings in SMON_SCN_TIME tab
le
KTF broadcast enq: TE - KTF broadcast KTF broadcasting
Temporary File enq: TF - contention Serializes dropping of a temporary file
Threshold Chain enq: TH - metric threshold evaluation Serializes threshold in-memory chain access
Auto Task Serialization enq: TK - Auto Task Serialization Lock held by MMON to prevent other MMON spawning o
f Autotask Slave
Auto Task Serialization enq: TK - Auto Task Slave Lockout Serializes spawned Autotask Slaves
Log Lock enq: TL - contention Serializes threshold log table read and update
DML enq: TM - contention Synchronizes accesses to an object
Temp Object enq: TO - contention Synchronizes DDL and DML operations on a temp obje
ct
Runtime Fixed Table Purge enq: TP - contention Lock held during purge and dynamic reconfiguration
of fixed tables.
Queue table enqueue enq: TQ - DDL contention TM access to the queue table
Queue table enqueue enq: TQ - DDL-INI contention Streams DDL on queue table
Queue table enqueue enq: TQ - INI contention TM access to the queue table
Queue table enqueue enq: TQ - TM contention TM access to the queue table
Temporary Segment enq: TS - contention Serializes accesses to temp segments
Tablespace enq: TT - contention Serializes DDL operations on tablespaces
Cross-Instance Transaction enq: TW - contention Lock held by one instance to wait for transactions
on all instances to finish
Transaction enq: TX - allocate ITL entry Allocating an ITL entry in order to begin a transa
ction
Transaction enq: TX - contention Lock held by a transaction to allow other transact
ions to wait for it
Transaction enq: TX - index contention Lock held on an index during a split to prevent ot
her operations on it
Transaction enq: TX - row lock contention Lock held on a particular row by a transaction to
prevent other transactions from modifying it
User-defined enq: UL - contention Lock used by user applications
Undo Segment enq: US - contention Lock held to perform DDL on the undo segment
AQ Notification Watermark enq: WA - contention Lock used for recovery when setting Watermark for
memory usage in AQ notifications
AWR Flush enq: WF - contention This enqueue is used to serialize the flushing of
snapshots
Write gather local enqueue enq: WG - delete fso acquire lobid local enqueue when deleting fso
Write gather local enqueue enq: WG - lock fso acquire lobid local enqueue when locking fso
Being Written Redo Log enq: WL - RAC-wide SGA contention Serialize access to RAC-wide SGA
Being Written Redo Log enq: WL - RFS global state contention Serialize access to RFS global state
Being Written Redo Log enq: WL - Test access/locking Testing redo transport access/locking
Being Written Redo Log enq: WL - contention Coordinates access to redo log files and archive l
ogs
WLM Plan Operations enq: WM - WLM Plan activation Synchronizes new WLM Plan activation
AWR Purge enq: WP - contention This enqueue handles concurrency between purging a
nd baselines
LNS archiving log enq: WR - contention Coordinates access to logs by Async LNS and ARCH/F
G
XDB Configuration enq: XC - XDB Configuration Lock obtained when incrementing XDB configuration
version number
Auto Online Exadata disks enq: XD - ASM disk OFFLINE Serialize OFFLINE Exadata disk operations
Auto Online Exadata disks enq: XD - ASM disk ONLINE Serialize ONLINE Exadata disk operations
Auto Online Exadata disks enq: XD - ASM disk drop/add Serialize Auto Drop/Add Exadata disk operations
AQ Notification No-Proxy enq: XH - contention Lock used for recovery when setting No Proxy Domai
ns for AQ HTTP notifications
ASM Extent Fault Lock enq: XL - fault extent map Keep multiple processes from faulting in the same
extent chunk
ASM Extent Relocation Enqueue enq: XQ - purification wait for relocation before doing block purificatio
n
ASM Extent Relocation Enqueue enq: XQ - recovery prevent relocation during _recovery_asserts checki
ng
ASM Extent Relocation Enqueue enq: XQ - relocation wait for recovery before doing relocation
Quiesce / Force Logging enq: XR - database force logging Lock held during database force logging mode
Quiesce / Force Logging enq: XR - quiesce database Lock held during database quiesce
Internal Test enq: XY - contention Lock used for internal testing
Audit Partition enq: ZA - add std audit table partition lock held to add partition to std audit table
FGA Partition enq: ZF - add fga audit table partition lock held to add partition to fga audit table
File Group enq: ZG - contention Coordinates file group operations
Compression Analyzer enq: ZH - compression analysis Synchronizes analysis and insert into compression$
, prevents multiple threads analyzing the same tab
le during a load
repopulation file access enq: ZX - repopulation file write synchronizes file operations during repopulation
Global Context Action enq: ZZ - update hash tables lock held for updating global context hash tables
Enqueue Type Description
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
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