Oracle Enqueues

The Enqueues Oracle metric are locks that serialize access to database resources. This event indicates that the session is waiting for a lock that is held by another session.

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

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


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