By v$lock, we could have a look at lock in every session. Lock have a lot of mode:

mode name   desc
0 none    
1 null    
2 Row-S   row sharing lock: share row
3 Row-X   row exclusive lock: for modify row
4 Share   share lock: block other DML
5 S/Row-X   shared row exclusive lock: block other transaction
6 exclusive   exclusive lock: independently access and use

lock type:

  • TM lock for parallel accessing table
  • TX transaction lock or row lock for parallel accessing row
  • MR media recover lock means database online
  • ST space transaction lock means due to bad file structure, some segments in database in increase or shrink SMON or merging free space nearby.


16 January 2015