V$Lock

V$LOCK

This view lists the locks currently held by the Oracle Database and outstanding requests for a lock or latch.

Column Datatype Description
ADDR RAW(4 | 8) Address of lock state object
KADDR RAW(4 | 8) Address of lock
SID NUMBER Identifier for session holding or acquiring the lock
TYPE VARCHAR2(2) Type of user or system lock
The locks on the user types are obtained by user applications. Any process that is blocking others is likely to be holding one of these locks. The user type locks are:
TM - DML enqueue
TX - Transaction enqueue
UL - User supplied
The locks on the system types are held for extremely short periods of time. The system type locks are listed in Table 6-1.
ID1 NUMBER Lock identifier #1 (depends on type)
ID2 NUMBER Lock identifier #2 (depends on type)
LMODE NUMBER Lock mode in which the session holds the lock:
0 - none
1 - null (NULL)
2 - row-S (SS)
3 - row-X (SX)
4 - share (S)
5 - S/Row-X (SSX)
6 - exclusive (X)
REQUEST NUMBER Lock mode in which the process requests the lock:
0 - none
1 - null (NULL)
2 - row-S (SS)
3 - row-X (SX)
4 - share (S)
5 - S/Row-X (SSX)
6 - exclusive (X)
CTIME NUMBER Time since current mode was granted
BLOCK NUMBER A value of either 0 or 1, depending on whether or not the lock in question is the blocker.
Table 6-1 Values for the TYPE Column: System Types

System Type Description
BL Buffer hash table instance
CF Control file schema global enqueue
CI Cross-instance function invocation instance
CU Cursor bind
DF datafile instance
DL Direct loader parallel index create
DM Mount/startup db primary/secondary instance
DR Distributed recovery process
DX Distributed transaction entry
FS File set
HW Space management operations on a specific segment
IN Instance number
IR Instance recovery serialization global enqueue
IS Instance state
IV Library cache invalidation instance
JQ Job queue
KK Thread kick
LA .. LP Library cache lock instance lock (A..P = namespace)
MM Mount definition global enqueue
MR Media recovery
NA..NZ Library cache pin instance (A..Z = namespace)
PF Password File
PI, PS Parallel operation
PR Process startup
QA..QZ Row cache instance (A..Z = cache)
RT Redo thread global enqueue
SC System change number instance
SM SMON
SN Sequence number instance
SQ Sequence number enqueue
SS Sort segment
ST Space transaction enqueue
SV Sequence number value
TA Generic enqueue
TS Temporary segment enqueue (ID2=0)
TS New block allocation enqueue (ID2=1)
TT Temporary table enqueue
UN User name
US Undo segment DDL
WL Being-written redo log instance

Reference:
http://docs.oracle.com/cd/B19306_01/server.102/b14237/dynviews_1147.htm#g1427852