Category: Technology

Indexing strategies with Jonathan Lewis

Today I was part of a NYOUG seminar about “Indexing Strategies” held by Mr. Jonathan Lewis himself. If somebody doesn’t know Jon Lewis, he is one of the top Oracle gurus on the entire planet with more than 25 years of Oracle experience. He probably used Oracle before I was even born (1985)! The very interesting fact however is that he actually never ever worked for Oracle but still has all the deep inside knowledge. Usually those gurus came out from Oracle or are still working for them. I guess the great amount of years dealing with Oracle helped him there.

However, Jonathan Lewis is also one of my top favorite because he shares his knowledge on his personal blog: http://jonathanlewis.wordpress.com In fact, Jons blog is the only one which I never can catch up with because he posts literally quicker than I got time to read his fabulous posts… reminds me that I should update my Blogroll.

The seminar itself was simply great. It was not free but those 230 bucks where totally worth it. Not only is Jon Lewis a great speaker – was the first time that I actually saw him – he also gave great detailed insights into indexes how they work, what is all possible with them and why Oracle is actually taking an index and much more important when it is not! . Furthermore he combined his sessions with some real world examples that he himself dealt with in the past which makes the whole thing much less theoretical.

Of course I won’t cover the whole seminar here, but I’ll end with some interesting things that I took out of it – some of which I got reminded again, some which were new for me:

  • Indexing means: Getting to data quickly
  • Indexes focus/compact data
  • There is always a Trade-Off between loading and querying performance
  • Index maintenance is expensive – it introduces costs
  • It’s all about precision
  • Non-unique indexes include the rowid automatically – for Oracle there are no non-unique indexes
  • Index compression can save a lots of space on repetitive columns
  • Index compression means elimination of duplicates
  • Primary key constraints don’t necessarily need unique key indexes but only indexes with the columns in the right order
  • Reverse indexes scatter entries accros the line, clustering factor can end up terrible
  • Don’t duplicate indexes – e.g. FK constraints can share the first columns of another index
  • Difference between tables and indexes: Index blocks have to be at the right place
  • Don’t trust Oracle – test everything!

 

Exadata, Exadata, Exadata

I’m currently in Menlo Park, California at the old Sun lab from Oracle and do some Exadata testing for work. Everything TOP SECRET of course so I cannot tell anything about it. But what I can do is to share some nice pics from the facilities and the boxes! 🙂

Oracle 11g R2 enqueue waits

Over 1 and a half year ago I posted the enqueue waits for Oracle 10g. Well, a lot has changed in 11g including the enqueue waits. This is the new list of enqueue waits in 11gR2:

Group 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 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 – PST split check Synchronizes check for Storage (PST) split in disk groups
ASM Enqueue enq: AM – background COD reservation Reserve a background COD entry
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
Service Operations enq: AS – service activation Synchronizes new service activation
Alter Tablespace enq: AT – contention Serializes ‘alter tablespace’ operations
Audit index file enq: AU – audit index file lock held to operate on the audit index file
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
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 – 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
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
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 – 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
LogicalStandby enq: SB – contention Synchronizes Logical Standby metadata 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) 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 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

For those who made it all to the bottom here a little extra:

While I just found the enqueue waits for 10g on the internet I managed to find out how to retrieve that information. And believe it or not – it’s available just over a simple query:

SELECT eq_name "Group", 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;