oracle lock mode
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
SMONor merging free space nearby.