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DBA_LOCK

lists all locks or latches held in the database, and all outstanding requests for a lock or latch.

Column	Datatype	NULL	Description
SESSION_ID	NUMBER	Session holding or acquiring the lock
LOCK_TYPE	VARCHAR2(26)	Lock type See Also: For a listing of lock types, see Appendix D, "Oracle Enqueue Names"
MODE HELD	VARCHAR2(40)	Lock mode
MODE REQUESTED	VARCHAR2(40)	Lock mode requested
LOCK_ID1	VARCHAR2(40)	Type-specific lock identifier, part 1
LOCK_ID2	VARCHAR2(40)	Type-specific lock identifier, part 2
LAST_CONVERT	NUMBER	The last convert
BLOCKING_OTHERS	VARCHAR2(40)	Whether the lock is currently blocking others

DBA_DML_LOCKS

lists all DML locks held in the database and all outstanding requests for a DML lock.

Column	Datatype	NULL	Description
SESSION_ID	NUMBER	Session holding or acquiring the lock
OWNER	VARCHAR2(30)	NOT NULL	Owner of the lock
NAME	VARCHAR2(30)	NOT NULL	Name of the lock
MODE_HELD	VARCHAR2(13)	The type of lock held. The values are: ROWS_S ( SS ): row share lock ROW-X ( SX ): row exclusive lock SHARE ( S ): share lock S/ROW-X ( SSX ): exclusive lock NONE : lock requested but not yet obtained
MODE_REQUESTED	VARCHAR2(13)	Lock request type. The values are: ROWS_S ( SS ): row share lock ROW-X ( SX ): row exclusive lock SHARE ( S ): share lock S/ROW-X ( SSX ): exclusive lock NONE : Lock identifier obtained; lock not held or requested
LAST_CONVERT	NUMBER	The last convert
BLOCKING_OTHERS	VARCHAR2(40)	Blocking others

DBA_DDL_LOCKS

lists all DDL locks held in the database and all outstanding requests for a DDL lock.

Column	Datatype	NULL	Description
SESSION_ID	NUMBER	Session identifier
OWNER	VARCHAR2(30)	Owner of the lock
NAME	VARCHAR2(30)	Name of the lock
TYPE	VARCHAR2(40)	Lock type: Cursor Table/Procedure/Type Body Trigger Index Cluster Java Source Java Resource Java Data
MODE_HELD	VARCHAR2(9)	Lock mode: None Null Share Exclusive
MODE_REQUESTED	VARCHAR2(9)	Lock request type: None Null Share Exclusive

DBA_WAITERS

shows all the sessions that are waiting for a lock.

Column	Datatype	NULL	Description
WAITING_SESSION	NUMBER	The waiting session
HOLDING_SESSION	NUMBER	The holding session
LOCK_TYPE	VARCHAR2(26)	The lock type
MODE_HELD	VARCHAR2(40)	The mode held
MODE_REQUESTED	VARCHAR2(40)	The mode requested
LOCK_ID1	VARCHAR2(40)	Lock ID 1
LOCK_ID2	VARCHAR2(40)	Lock ID 2

DBA_BLOCKERS

displays a session if it is not waiting for a locked object but is holding a lock on an object for which another session is waiting.

Column	Datatype	NULL	Description
HOLDING_SESSION	NUMBER	Session holding a lock

Reference