D Oracle Enqueue Names

This appendix lists Oracle enqueues. 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.

A resource uniquely identifies an object that can be locked by different sessions within an instance (local resource) or between instances (global resource). Each session that tries to lock the resource will have an enqueue on the resource.


The names of enqueues and their definitions may change from release to release.

See Also:


The Oracle enqueues are:

  • BL, Buffer Cache Management

  • BR, Backup/Restore

  • CF, Controlfile Transaction

  • CI, Cross-instance Call Invocation

  • CU, Bind Enqueue

  • DF, Datafile

  • DL, Direct Loader Index Creation

  • DM, Database Mount

  • DR, Distributed Recovery Process

  • DW, SecureFiles

  • DX, Distributed Transaction

  • FP, File Object

  • FS, File Set

  • HW, High-Water Lock

  • IN, Instance Number

  • IR, Instance Recovery

  • IS, Instance State

  • IV, Library Cache Invalidation

  • JI, Enqueue used during AJV snapshot refresh

  • JQ, Job Queue

  • KK, Redo Log "Kick"

  • KP, contention in Oracle Data Pump startup and shutdown processes

  • KO, Multiple Object Checkpoint

  • L[A-P], Library Cache Lock

  • LS, Log Start or Switch

  • MM, Mount Definition

  • MR, Media Recovery

  • N[A-Z], Library Cache Pin


  • PF, Password File

  • PI, Parallel Slaves

  • PR, Process Startup

  • PS, Parallel Slave Synchronization

  • Q[A-Z], Row Cache

  • RO, Object Reuse

  • RT, Redo Thread

  • RW, Row Wait

  • SC, System Change Number

  • SM, SMON

  • SN, Sequence Number

  • SQ, Sequence Number Enqueue

  • SR, Synchronized Replication

  • SS, Sort Segment

  • ST, Space Management Transaction

  • SV, Sequence Number Value

  • TA, Transaction Recovery

  • TC, Thread Checkpoint

  • TE, Extend Table

  • TM, DML Enqueue

  • TO, Temporary Table Object Enqueue

  • TS, Temporary Segment (also TableSpace)

  • TT, Temporary Table

  • TX, Transaction

  • UL, User-defined Locks

  • UN, User Name

  • US, Undo Segment, Serialization

  • WL, Being Written Redo Log

  • XA, Instance Attribute Lock

  • XI, Instance Registration Lock

  • ZA, Exclusive Lock When Moving Audit Table