Wait events Oracle 11g – enqueues

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Enqueues – are shared memory structures (locks) that serialize access to database resources. They can be associated with a session or transaction. Enqueue names are displayed in the LOCK_TYPE column of the DBA_LOCK and DBA_LOCK_INTERNAL data dictionary views.

In case your session is slow you can always check what it’s waiting for in v$session table.

This query just shows sessions waiting for enqueue resources

SELECT sid, serial#, event, wait_class 
FROM v$session WHERE event LIKE 'enq:%';

To get description of an enqueue resource use following query.

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 name Enqueue type Description
Auto BMR enq: AB – ABMR process initialized Lock held to ensure that ABMR process is initialized
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 advisor task
Analytic Workspace Generation enq: AG – contention Synchronizes generation use of a particular workspace
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 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 hash
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 instance shutdown
MultiWriter Object Access enq: AO – contention Synchornizes access to objects and scalar variables
SPM Autopurge enq: AP – contention This enqueue is used to serialize the purging of SQL 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 workspace
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 instances
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 physical size during RMAN backup
Backup/Restore enq: BR – multi-section restore header Lock held to serialize file header access during multi-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 the headers at the same time
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 comparison
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 registrations
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 registrations enq: CQ – contention Serializes access to cleanup client query cache registrations
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 resources
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 thread
Block Change Tracking enq: CT – reading Lock held to ensure that change tracking data remains in existence until a reader is done with it
Block Change Tracking enq: CT – state Lock held while enabling or disabling change tracking, 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 tracking in RAC
Block Change Tracking enq: CT – state change gate 2 Lock held while enabling or disabling change tracking 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 supplementallogging 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 operation
Database Suspend enq: DS – contention Prevents a database suspend during LMON reconfiguration
Default Temporary Tablespace enq: DT – contention Serializes changing the default temporary table spaceand 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 blcoks 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 relocation 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 operations 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 the 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 parallel inserts
Segment High Water Mark enq: HW – contention Lock used to broker the high water mark during parallel inserts
Internal enq: IA – contention
NID enq: ID – contention Lock held to prevent other processes from performing controlfile transaction while NID is running
Label Security enq: IL – contention Synchronizes accesses to internal label data structures
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 shutdown immediate
Instance State enq: IS – contention Enqueue used to synchronize instance state changes
In-Mem Temp Table Meta Creation enq: IT – contention Synchronizes accesses to a temp object’s metadata
Job Queue Date enq: JD – contention Synchronizes dates between job queue coordinator and slave processes
Materialized View enq: JI – contention Lock held during materialized view operations (like 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 Manager plan
Materialized View Log DDL enq: MD – contention Lock held during materialized view log DDL statements
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 and prevents multiple instances from preparing the same 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 – standby role transition Lock used to disallow concurrent standby role transition attempt
Materialized View Refresh Log enq: MS – contention Lock held during materialized view refresh to setup MV log
Online Datafile Move enq: MV – datafile move Held during online datafile move operation or cleanup
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 server information request when an instance is starting 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 HTTP notifications
Remote PX Process Spawn Status enq: PI – contention Communicates remote Parallel Execution Server Process creation status
Transportable Tablespace enq: PL – contention Coordinates plug-in operation of transportable tablespaces
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 Table enq: PT – contention Synchronizes access to ASM PST metadata
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 DBWR 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 current
Data Guard Broker enq: RF – FSFO Observer Heartbeat Captures recent Fast-Start Failover Observer heartbeat 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 automatically 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 datablock is repaired from mirror
Workload Capture and Replay enq: RR – contention Concurrent invocation of DBMS_WORKLOAD_* package API
Reclaimable Space enq: RS – file delete Lock held to prevent file from accessing during space 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 space
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 reusing 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 indicate mounted or open status
Redo Thread enq: RT – thread internal enable/disable Thread locks held by CKPT to synchronize thread enable 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 viewwhile updating materialized view flags in detail tables
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 operations
Session Migration enq: SE – contention Synchronizes transparent session migration operations
AQ Notification Sender enq: SF – contention Lock used for recovery when setting Sender for AQ e-mail notifications
Active Session History Flushing enq: SH – contention Should seldom see this contention as this Enqueue 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 process
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 Shared Object Manager)
Spare Enqueue enq: SP – contention 1 (1) due to one-off patch
Spare Enqueue enq: SP – contention 2 (2) due to one-off patch
Spare Enqueue enq: SP – contention 3 (3) due to one-off patch
Spare Enqueue 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 dictionary-managed tablespaces
SaveUndo Segment enq: SU – contention Serializes access to SaveUndo Segment
Suspend Writes enq: SW – contention Coordinates the ‘alter system suspend’ operation
Instance Undo enq: TA – contention Serializes operations on undo segments and undo tablespaces
SQL Tuning Base Existence Cache enq: TB – SQL Tuning Base Cache Load Synchronizes writes to the SQL Tuning Base Existence Cache
SQL Tuning Base Existence Cache enq: TB – SQL Tuning Base Cache Update Synchronizes writes to the SQL Tuning Base Existence 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 table
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 of 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 object
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 transaction
Transaction enq: TX – contention Lock held by a transaction to allow other transactions to wait for it
Transaction enq: TX – index contention Lock held on an index during a split to prevent other 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 logs
WLM Plan Operations enq: WM – WLM Plan activation Synchronizes new WLM Plan activation
AWR Purge enq: WP – contention This enqueue handles concurrency between purging and baselines
LNS archiving log enq: WR – contention Coordinates access to logs by Async LNS and ARCH/FG
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 Domains 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 purification
ASM Extent Relocation Enqueue enq: XQ – recovery prevent relocation during _recovery_asserts checking
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 table during a load
Global Context Action enq: ZZ – update hash tables lock held for updating global context hash tables

Have a fun 🙂

Tomasz

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