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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.
If you are working on 11203 database the following table lists all the enqueue waits in Oracle 11.2.0.3 and describes what the enqueue is for. Please email me if you have any questions.
WAIT_CLASS NAME DESCRIPTION
---------------- ------------------------------- -------------------------------
Administrative enq: TW - contention Lock held by one instance to wa
it for transactions on all inst
ances to finish
Administrative enq: ZG - contention Coordinates file group operatio
ns
Administrative enq: DB - contention Synchronizes modification of da
tabase wide supplementallogging
attributes
Administrative enq: MV - datafile move Held during online datafile mov
e operation or cleanup
Application enq: RC - Result Cache: Content Coordinates access to a result-
ion set
Application enq: PW - flush prewarm buffers Direct Load needs to flush prew
armed buffers if DBWR 0 holds e
nqueue
Application enq: TM - contention Synchronizes accesses to an obj
ect
Application enq: RO - contention Coordinates flushing of multipl
e objects
Application enq: RO - fast object reuse Coordinates fast object reuse
Application enq: KO - fast object checkpoin Coordinates fast object checkpo
t int
Application enq: UL - contention Lock used by user applications
Application enq: TX - row lock contention Lock held on a particular row b
y a transaction to prevent othe
r transactions from modifying i
t
Commit enq: BB - 2PC across RAC instan 2PC distributed transaction bra
ces nch across RAC instances
Concurrency enq: HV - contention Lock used to broker the high wa
ter mark during parallel insert
s
Concurrency enq: TX - index contention Lock held on an index during a
split to prevent other operatio
ns on it
Concurrency enq: WG - lock fso acquire lobid local enqueue whe
n locking fso
Configuration enq: SQ - contention Lock to ensure that only one pr
ocess can replenish the sequenc
e cache
Configuration enq: HW - contention Lock used to broker the high wa
ter mark during parallel insert
s
Configuration enq: ST - contention Synchronizes space management a
ctivities in dictionary-managed
tablespaces
Configuration enq: TX - allocate ITL entry Allocating an ITL entry in orde
r to begin a transaction
Configuration enq: SS - contention Ensures that sort segments crea
ted during parallel DML operati
ons aren't prematurely cleaned
up
Other null event
Other enq: WM - WLM Plan activation Synchronizes new WLM Plan activ
ation
Other enq: CI - contention Coordinates cross-instance func
tion invocations
Other enq: PR - contention Synchronizes process startup
Other enq: PE - contention Synchronizes system parameter u
pdates
Other enq: PG - contention Synchronizes global system para
meter updates
Other enq: FP - global fob contention Synchronizes various File Objec
t(FOB) operations
Other enq: RE - block repair contenti Synchronize block repair/resilv
on ering operations
Other enq: BM - clonedb bitmap file w synchronizes clonedb bitmap fil
rite e operations
Other enq: KM - contention Synchronizes various Resource M
anager operations
Other enq: KT - contention Synchronizes accesses to the cu
rrent Resource Manager plan
Other enq: CA - contention Synchronizes various IO calibra
tion runs
Other enq: KD - determine DBRM master Determine DBRM master
Other enq: PV - syncstart Synchronizes slave start_shutdo
wn
Other enq: PV - syncshut Synchronizes instance shutdown_
slvstart
Other enq: SP - contention 1 (1) due to one-off patch
Other enq: SP - contention 2 (2) due to one-off patch
Other enq: SP - contention 3 (3) due to one-off patch
Other enq: SP - contention 4 (4) due to one-off patch
Other enq: FM - contention Synchronizes access to global f
ile mapping state
Other enq: XY - contention Lock used for internal testing
Other enq: AS - service activation Synchronizes new service activa
tion
Other enq: PD - contention Prevents others from updating t
he same property
Other enq: RU - contention Serializes rolling migration op
erations
Other enq: RU - waiting Results of rolling migration CI
C
Other enq: MX - sync storage server i Lock held to generate a respons
nfo e to the storage server informa
tion request when an instance i
s starting up
Other enq: CF - contention Synchronizes accesses to the co
ntrolfile
Other enq: SW - contention Coordinates the 'alter system s
uspend' operation
Other enq: DS - contention Prevents a database suspend dur
ing LMON reconfiguration
Other enq: TC - contention Lock held to guarantee uniquene
ss of a tablespace checkpoint
Other enq: TC - contention2 Lock of setup of a unqiue table
space checkpoint in null mode
Other enq: PW - perwarm status in dbw DBWR 0 holds enqueue indicating
0 prewarmed buffers present in c
ache
Other enq: CR - block range reuse ckp Coordinates fast block range re
t use ckpt
Other enq: WL - Test access/locking Testing redo transport access/l
ocking
Other enq: WL - RAC-wide SGA contenti Serialize access to RAC-wide SG
on A
Other enq: WL - RFS global state cont Serialize access to RFS global
ention state
Other enq: WR - contention Coordinates access to logs by A
sync LNS and ARCH/FG
Other enq: WL - contention Coordinates access to redo log
files and archive logs
Other enq: RN - contention Coordinates nab computations of
online logs during recovery
Other enq: DF - contention Enqueue held by foreground or D
BWR when a datafile is brought
online in RAC
Other enq: IS - contention Enqueue used to synchronize ins
tance state changes
Other enq: FS - contention Enqueue used to synchronize rec
overy and file operations or sy
nchronize dictionary check
Other enq: DM - contention Enqueue held by foreground or D
BWR to syncrhonize database mou
nt/open with other operations
Other enq: RP - contention Enqueue held when resilvering i
s needed or when datablock is r
epaired from mirror
Other enq: RT - contention Thread locks held by LGWR, DBW0
, and RVWR to indicate mounted
or open status
Other enq: RT - thread internal enabl Thread locks held by CKPT to sy
e/disable nchronize thread enable and dis
able
Other enq: IR - contention Synchronizes instance recovery
Other enq: IR - contention2 Synchronizes parallel instance
recovery and shutdown immediate
Other enq: MR - contention Lock used to coordinate media r
ecovery with other uses of data
files
Other enq: MR - standby role transiti Lock used to disallow concurren
on t standby role transition attem
pt
Other enq: BR - file shrink Lock held to prevent file from
decreasing in physical size dur
ing RMAN backup
Other enq: BR - proxy-copy Lock held to allow cleanup from
backup mode during an RMAN pro
xy-copy backup
Other enq: BR - multi-section restore Lock held to serialize file hea
header der access during multi-section
restore
Other enq: BR - multi-section restore Lock held to serialize section
section access during multi-section res
tore
Other enq: BR - space info datafile h Lock held to prevent multiple p
dr update rocess to update the headers at
the same time
Other enq: BR - request autobackup Lock held to request controlfil
e autobackups
Other enq: BR - perform autobackup Lock held to perform a new cont
rolfile autobackup
Other enq: ID - contention Lock held to prevent other proc
esses from performing controlfi
le transaction while NID is run
ning
Other enq: AB - ABMR process start/st Lock held to ensure that only o
op ne ABMR is started in the clust
er
Other enq: AB - ABMR process initiali Lock held to ensure that ABMR p
zed rocess is initialized
Other enq: MN - contention Synchronizes updates to the Log
Miner dictionary and prevents m
ultiple instances from preparin
g the same LogMiner session
Other enq: PL - contention Coordinates plug-in operation o
f transportable tablespaces
Other enq: SB - logical standby metad Synchronizes Logical Standby me
ata tadata operations
Other enq: SB - table instantiation Synchronizes table instantiatio
n and EDS operations
Other enq: XR - quiesce database Lock held during database quies
ce
Other enq: XR - database force loggin Lock held during database force
g logging mode
Other enq: CT - global space manageme Lock held during change trackin
nt g space management operations t
hat affect the entire change tr
acking file
Other enq: CT - local space managemen Lock held during change trackin
t g space management operations t
hat affect just the data for on
e thread
Other enq: CT - change stream ownersh Lock held by one instance while
ip change tracking is enabled, to
guarantee access to thread-spe
cific resources
Other enq: CT - state Lock held while enabling or dis
abling change tracking, to ensu
re that it is only enabled or d
isabled by one user at a time
Other enq: CT - state change gate 1 Lock held while enabling or dis
abling change tracking in RAC
Other enq: CT - state change gate 2 Lock held while enabling or dis
abling change tracking in RAC
Other enq: CT - CTWR process start/st Lock held to ensure that only o
op ne CTWR process is started in a
single instance
Other enq: CT - reading Lock held to ensure that change
tracking data remains in exist
ence until a reader is done wit
h it
Other enq: RS - file delete Lock held to prevent file from
accessing during space reclaima
tion
Other enq: RS - record reuse Lock held to prevent file from
accessing while reusing circula
r record
Other enq: RS - prevent file delete Lock held to prevent deleting f
ile to reclaim space
Other enq: RS - prevent aging list up Lock held to prevent aging list
date update
Other enq: RS - persist alert level Lock held to make alert level p
ersistent
Other enq: RS - read alert level Lock held to read alert level
Other enq: RS - write alert level Lock held to write alert level
Other enq: FL - Flashback database lo Synchronization
g
Other enq: FL - Flashback db command Enqueue used to synchronize Fla
shback Database and and deletio
n of flashback logs.
Other enq: FD - Marker generation Synchronization
Other enq: FD - Tablespace flashback Synchronization
on/off
Other enq: FD - Flashback coordinator Synchronization
Other enq: FD - Flashback on/off Synchronization
Other enq: FD - Restore point create/ Synchronization
drop
Other enq: FD - Flashback logical ope Synchronization
rations
Other enq: TA - contention Serializes operations on undo s
egments and undo tablespaces
Other enq: TX - contention Lock held by a transaction to a
llow other transactions to wait
for it
Other enq: US - contention Lock held to perform DDL on the
undo segment
Other enq: IM - contention for blr Serializes block recovery for I
MU txn
Other enq: TD - KTF dump entries KTF dumping time/scn mappings i
n SMON_SCN_TIME table
Other enq: TE - KTF broadcast KTF broadcasting
Other enq: CN - race with txn during registration
Other enq: CN - race with reg during transaction commit to se
e concurrent registrations
Other enq: CN - race with init during descriptor initializatio
n
Other enq: CO - master slave det enqueue held be Master in Clean
out Optim
Other enq: FE - contention Serializes flashback archive re
covery
Other enq: TF - contention Serializes dropping of a tempor
ary file
Other enq: DT - contention Serializes changing the default
temporary table spaceand user
creation
Other enq: TS - contention Serializes accesses to temp seg
ments
Other enq: FB - contention Ensures that only one process c
an format data blcoks in auto s
egment space managed tablespace
s
Other enq: SK - contention Serialize shrink of a segment
Other enq: DW - contention Serialize in memory dispenser o
perations
Other enq: SU - contention Serializes access to SaveUndo S
egment
Other enq: TT - contention Serializes DDL operations on ta
blespaces
Other enq: SJ - Slave Task Cancel Serializes cancelling task exec
uted by slave process
Other enq: DL - contention Lock to prevent index DDL durin
g direct load
Other enq: HQ - contention Synchronizes the creation of ne
w queue IDs
Other enq: HP - contention Synchronizes accesses to queue
pages
Other enq: WG - delete fso acquire lobid local enqueue whe
n deleting fso
Other enq: SL - get lock sending lock req to LCK0
Other enq: SL - escalate lock sending lock escalate to LCK0
Other enq: SL - get lock for undo sending lock req for undo to LC
K0
Other enq: ZH - compression analysis Synchronizes analysis and inser
t into compression$, prevents m
ultiple threads analyzing the s
ame table during a load
Other enq: DV - contention Synchronizes access to lower-ve
rsion Diana (PL/SQL intermediat
e representation)
Other enq: SO - contention Synchronizes access to Shared O
bject (PL/SQL Shared Object Man
ager)
Other enq: TP - contention Lock held during purge and dyna
mic reconfiguration of fixed ta
bles.
Other enq: RW - MV metadata contentio Lock held by CREATE/ALTER/DROP
n materialized viewwhile updating
materialized view flags in det
ail tables
Other enq: OC - contention Synchronizes write accesses to
the outline cache
Other enq: OL - contention Synchronizes accesses to a part
icular outline name
Other enq: CU - contention Recovers cursors in case of dea
th while compiling
Other enq: AE - lock Prevent Dropping an edition in
use
Other enq: PF - contention Synchronizes accesses to the pa
ssword file
Other enq: IL - contention Synchronizes accesses to intern
al label data structures
Other enq: CL - drop label Synchronizes accesses to label
cache when dropping a label
Other enq: CL - compare labels Synchronizes accesses to label
cache for label comparison
Other enq: MK - contention changing values in enc$
Other enq: OW - initialization initializing the wallet context
Other enq: OW - termination terminate the wallet context
Other enq: RK - set key wallet master key rekey
Other enq: RL - RAC wallet lock RAC wallet lock
Other enq: ZZ - update hash tables lock held for updating global c
ontext hash tables
Other enq: ZA - add std audit table p lock held to add partition to s
artition td audit table
Other enq: ZF - add fga audit table p lock held to add partition to f
artition ga audit table
Other enq: DX - contention Serializes tightly coupled dist
ributed transaction branches
Other enq: DR - contention Serializes the active distribut
ed recovery operation
Other enq: JD - contention Synchronizes dates between job
queue coordinator and slave pro
cesses
Other enq: JQ - contention Lock to prevent multiple instan
ces from running a single job
Other enq: OD - Serializing DDLs Lock to prevent concurrent onli
ne DDLs
Other enq: MD - contention Lock held during materialized v
iew log DDL statements
Other enq: MS - contention Lock held during materialized v
iew refresh to setup MV log
Other enq: PI - contention Communicates remote Parallel Ex
ecution Server Process creation
status
Other enq: PS - contention Parallel Execution Server Proce
ss reservation and synchronizat
ion
Other enq: AY - contention Affinity Dictionary test affini
ty synchronization
Other enq: TO - contention Synchronizes DDL and DML operat
ions on a temp object
Other enq: IT - contention Synchronizes accesses to a temp
object's metadata
Other enq: BF - allocation contention Allocate a bloom filter in a pa
rallel statement
Other enq: BF - PMON Join Filter clea PMON bloom filter recovery
nup
Other enq: RD - RAC load update RAC load info
Other enq: KP - contention Synchronizes kupp process start
up
Other enq: SR - contention Coordinates replication / strea
ms operations
Other enq: SI - contention Prevents multiple streams tabel
instantiations
Other enq: IA - contention
Other enq: JI - contention Lock held during materialized v
iew operations (like refresh, a
lter) to prevent concurrent ope
rations on the same materialize
d view
Other enq: AT - contention Serializes 'alter tablespace' o
perations
Other enq: CQ - contention Serializes access to cleanup cl
ient query cache registrations
Other enq: SE - contention Synchronizes transparent sessio
n migration operations
Other enq: TQ - TM contention TM access to the queue table
Other enq: TQ - DDL contention TM access to the queue table
Other enq: TQ - INI contention TM access to the queue table
Other enq: TQ - DDL-INI contention Streams DDL on queue table
Other enq: DP - contention Synchronizes access to LDAP par
ameters
Other enq: MH - contention Lock used for recovery when set
ting Mail Host for AQ e-mail no
tifications
Other enq: ML - contention Lock used for recovery when set
ting Mail Port for AQ e-mail no
tifications
Other enq: PH - contention Lock used for recovery when set
ting Proxy for AQ HTTP notifica
tions
Other enq: SF - contention Lock used for recovery when set
ting Sender for AQ e-mail notif
ications
Other enq: XH - contention Lock used for recovery when set
ting No Proxy Domains for AQ HT
TP notifications
Other enq: WA - contention Lock used for recovery when set
ting Watermark for memory usage
in AQ notifications
Other enq: CX - TEXT: Index Specific Index Specific Lock on CTX inde
Lock x
Other enq: OT - TEXT: Generic Lock CTX Generic Locks
Other enq: XC - XDB Configuration Lock obtained when incrementing
XDB configuration version numb
er
Other enq: RF - synch: DG Broker meta Ensures r/w atomicity of DG con
data figuration metadata
Other enq: RF - atomicity Ensures atomicity of log transp
ort setup
Other enq: RF - synchronization: aifo Synchronizes apply instance fai
master lure detection and failover ope
ration
Other enq: RF - new AI Synchronizes selection of the n
ew apply instance
Other enq: RF - synchronization: crit Synchronizes critical apply ins
ical ai tance among primary instances
Other enq: RF - RF - Database Automat Means for detecting when databa
ic Disable se is being automatically disab
led
Other enq: RF - FSFO Observer Heartbe Captures recent Fast-Start Fail
at over Observer heartbeat informa
tion
Other enq: RF - DG Broker Current Fil Identifies which configuration
e ID metadata file is current
Other enq: RF - FSFO Primary Shutdown Records when FSFO Primary Shutd
suspended own is suspended
Other enq: AW - AW$ table lock Global access synchronization t
o the AW$ table
Other enq: AW - AW state lock Row lock synchronization for th
e AW$ table
Other enq: AW - user access for AW Synchronizes user accesses to a
particular workspace
Other enq: AW - AW generation lock In-use generation state for a p
articular workspace
Other enq: AG - contention Synchronizes generation use of
a particular workspace
Other enq: AO - contention Synchornizes access to objects
and scalar variables
Other enq: OQ - xsoqhiAlloc Synchronizes access to olapi hi
story allocation
Other enq: OQ - xsoqhiFlush Synchronizes access to olapi hi
story flushing
Other enq: OQ - xsoq*histrecb Synchronizes access to olapi hi
story parameter CB
Other enq: OQ - xsoqhiClose Synchronizes access to olapi hi
story closing
Other enq: OQ - xsoqhistrecb Synchronizes access to olapi hi
story globals
Other enq: AM - client registration Registers DB instance to ASM cl
ient state object hash
Other enq: AM - shutdown Prevent DB instance registratio
n during ASM instance shutdown
Other enq: AM - rollback COD reservat Reserve a rollback COD entry
ion
Other enq: AM - background COD reserv Reserve a background COD entry
ation
Other enq: AM - ASM cache freeze Start ASM cache freeze
Other enq: AM - ASM ACD Relocation Block ASM cache freeze
Other enq: AM - group use Client group use
Other enq: AM - group block ASM group block
Other enq: AM - ASM File Destroy Prevent same file deletion race
Other enq: AM - ASM User Prevents a user from being drop
ped if it owns any open files
Other enq: AM - ASM Password File Upd Allow one ASM password file upd
ate ate per cluster at a time
Other enq: AM - ASM Amdu Dump Allow only one AMDU dump when b
lock read failure
Other enq: AM - disk offline Synchronizes disk offlines
Other enq: AM - ASM reserved Check id1 of call for specific
purpose
Other enq: AM - block repair Serializes block repairs
Other enq: AM - ASM disk based alloc/ Synchronizes disk based allocat
dealloc ions/deallocations
Other enq: AM - ASM file descriptor Serializes access to ASM file d
escriptors
Other enq: AM - ASM file relocation Serializes file relocation shri
nk and drop
Other enq: CM - gate serialize access to instance en
queue
Other enq: CM - instance indicate ASM diskgroup is mount
ed
Other enq: CM - diskgroup dismount serialize asm diskgroup dismoun
t
Other enq: XQ - recovery prevent relocation during _reco
very_asserts checking
Other enq: XQ - relocation wait for recovery before doing
relocation
Other enq: XQ - purification wait for relocation before doin
g block purification
Other enq: AD - allocate AU Synchronizes accesses to a spec
ific ASM disk AU
Other enq: AD - deallocate AU Synchronizes accesses to a spec
ific ASM disk AU
Other enq: AD - relocate AU Synchronizes accesses to a spec
ific ASM disk AU
Other enq: DO - disk online Synchronizes disk onlines and t
heir recovery
Other enq: DO - disk online recovery Synchronizes disk onlines and t
heir recovery
Other enq: DO - Staleness Registry cr Synchronizes Staleness Registry
eate creation
Other enq: DO - startup of MARK proce Synchronizes startup of MARK pr
ss ocess
Other enq: DO - disk online operation Represents an active disk onlin
e operation
Other enq: XL - fault extent map Keep multiple processes from fa
ulting in the same extent chunk
Other enq: DG - contention Synchronizes accesses to ASM di
sk groups
Other enq: DD - contention Synchronizes local accesses to
ASM disk groups
Other enq: HD - contention Serializes accesses to ASM SGA
data structures
Other enq: DN - contention Serializes group number generat
ions
Other enq: FA - access file Synchronizes accesses to open A
SM files
Other enq: RX - relocate extent Synchronizes relocating ASM ext
ents
Other enq: RX - unlock extent Synchronizes unlocking ASM exte
nts
Other enq: FR - contention begin recovery of disk group
Other enq: FR - use the thread indicate this ACD thread is ali
ve
Other enq: FR - recover the thread wait for lock domain detach
Other enq: FG - serialize ACD relocat only 1 process in the cluster m
e ay do ACD relocation in a disk
group
Other enq: FG - FG redo generation en resolve race condition to acqui
q race re Disk Group Redo Generation E
nqueue
Other enq: FG - LGWR redo generation resolve race condition to acqui
enq race re Disk Group Redo Generation E
nqueue
Other enq: FT - allow LGWR writes allow LGWR to generate redo in
this thread
Other enq: FT - disable LGWR writes prevent LGWR from generating re
do in this thread
Other enq: FC - open an ACD thread LGWR opens an ACD thread
Other enq: FC - recover an ACD thread SMON recovers an ACD thread
Other enq: FX - issue ACD Xtnt Reloca ARB relocates ACD extent
tion CIC
Other enq: RB - contention Serializes ASM rollback recover
y operations
Other enq: PT - contention Synchronizes access to ASM PST
metadata
Other enq: KQ - access ASM attribute Synchronization of ASM cached a
ttributes
Other enq: AV - persistent DG number prevent DG number collisions
Other enq: AV - volume relocate Serialize relocating volume ext
ents
Other enq: AV - AVD client registrati Serialize inst reg and first DG
on use
Other enq: AV - add/enable first volu Serialize taking the AVD DG enq
me in DG ueue
Other enq: WF - contention This enqueue is used to seriali
ze the flushing of snapshots
Other enq: WP - contention This enqueue handles concurrenc
y between purging and baselines
Other enq: FU - contention This enqueue is used to seriali
ze the capture of the DB Featur
e Usage and High Wate
r Mark Statistics
Other enq: MW - contention This enqueue is used to seriali
ze the calibration of the
manageability schedules wi
th the Maintenance Window
Other enq: TB - SQL Tuning Base Cache Synchronizes writes to the SQL
Update Tuning Base Existence Cache
Other enq: TB - SQL Tuning Base Cache Synchronizes writes to the SQL
Load Tuning Base Existence Cache
Other enq: SH - contention Should seldom see this contenti
on as this Enqueue is always a
cquired in no-wait mode
Other enq: AF - task serialization This enqueue is used to seriali
ze access to an advisor task
Other enq: MO - contention Serialize MMON operations for r
estricted sessions
Other enq: TL - contention Serializes threshold log table
read and update
Other enq: TH - metric threshold eval Serializes threshold in-memory
uation chain access
Other enq: TK - Auto Task Serializati Lock held by MMON to prevent ot
on her MMON spawning of Autotask S
lave
Other enq: TK - Auto Task Slave Locko Serializes spawned Autotask Sla
ut ves
Other enq: RR - contention Concurrent invocation of DBMS_W
ORKLOAD_* package API
Other enq: JS - contention Synchronizes accesses to the jo
b cache
Other enq: JS - job run lock - synchr Lock to prevent job from runnin
onize g elsewhere
Other enq: JS - job recov lock Lock to recover jobs running on
crashed RAC inst
Other enq: JS - queue lock Lock on internal scheduler queu
e
Other enq: JS - sch locl enqs Scheduler non-global enqueues
Other enq: JS - q mem clnup lck Lock obtained when cleaning up
q memory
Other enq: JS - evtsub add Lock got when adding subscriber
to event q
Other enq: JS - evtsub drop Lock got when dropping subscrib
er to event q
Other enq: JS - wdw op Lock got when doing window open
/close
Other enq: JS - evt notify Lock got during event notificat
ion
Other enq: JS - aq sync Scheduler evt code and AQ sync
Other enq: XD - ASM disk drop/add Serialize Auto Drop/Add Exadata
disk operations
Other enq: XD - ASM disk ONLINE Serialize ONLINE Exadata disk o
perations
Other enq: XD - ASM disk OFFLINE Serialize OFFLINE Exadata disk
operations
Scheduler enq: JX - cleanup of queue release SQL statement resources
Scheduler enq: JX - SQL statement queue statement
303 rows selected.
If you are in any version, you can run the following query:
select a.wait_class, a.name, b.KSQSTEXPL description
from
v$event_name a,
x$ksqst b
where a.EVENT#=b.KSQSTEVIDX
order by a.wait_class;