v$lock
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
–我们主要关注TX和TM两种类型的锁
–UL锁用户自己定义的，一般很少会定义，基本不用关注
–其它均为系统锁，会很快自动释放，不用关注
ID1 NUMBER Lock identifier #1 (depends on type)
ID2 NUMBER Lock identifier #2 (depends on type)
—当lock type 为TM时，id1为DML-locked object的object_id
—当lock type 为TX时，id1为usn+slot，而id2为seq。
–当lock type为其它时，不用关注
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)
–大于0时表示当前会话以某种模式占有该锁，等于0时表示当前会话正在等待该锁资源，即表示该会话被阻塞。
–往往在发生TX锁时，伴随着TM锁，比如一个sid=9会话拥有一个TM锁，一般会拥有一个或几个TX锁，但他们的id1和id2是不同的，请注意
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)
–大于0时，表示当前会话被阻塞，其它会话占有改锁的模式
CTIME NUMBER Time since current mode was granted
BLOCK NUMBER The lock is blocking another lock
0, ‘Not Blocking’, /* Not blocking any other processes */
1, ‘Blocking’, /* This lock blocks other processes */
2, ‘Global’, /* This lock is global, so we can’t tell */
–该锁是否阻塞了另外一个锁
