intention lock 意向锁，表明有事务正在或者打算锁住一行记录
record lock 行所，分为排他锁和共享锁
gap lock 锁住索引之间的间隙
next key lock：record lock + gap lock
for example
id :0,5,10,15,20,25
unique,a
index,b
| id=10 |
|---|
| index_name | lock_type | lock_mode | lock_status | lock_data |
| NULL | TABLE | IX | GRANTED | NULL |
| PRIMARY | RECORD | X,REC_NOT_GAP | GRANTED | 10 |
| a=10 |
|---|
| index_name | lock_type | lock_mode | lock_status | lock_data |
| NULL | TABLE | IX | GRANTED | NULL |
| test_a_uindex | RECORD | X,REC_NOT_GAP | GRANTED | 10, 10 |
| PRIMARY | RECORD | X,REC_NOT_GAP | GRANTED | 10 |
| b=10 |
|---|
| index_name | lock_type | lock_mode | lock_status | lock_data |
| NULL | TABLE | IX | GRANTED | NULL |
| test_t_index | RECORD | X | GRANTED | 10, 10 |
| PRIMARY | RECORD | X,REC_NOT_GAP | GRANTED | 10 |
| test_t_index | RECORD | X,GAP | GRANTED | 15, 15 |
| id=11 |
|---|
| index_name | lock_type | lock_mode | lock_status | lock_data |
| NULL | TABLE | IX | GRANTED | NULL |
| PRIMARY | RECORD | X,GAP | GRANTED | 15 |
| a=11 |
|---|
| index_name | lock_type | lock_mode | lock_status | lock_data |
| NULL | TABLE | IX | GRANTED | NULL |
| test_a_uindex | RECORD | X,GAP | GRANTED | 15, 15 |
| b=11 |
|---|
| index_name | lock_type | lock_mode | lock_status | lock_data |
| NULL | TABLE | IX | GRANTED | NULL |
| test_t_index | RECORD | X,GAP | GRANTED | 15, 15 |
| id>11 |
|---|
| index_name | lock_type | lock_mode | lock_status | lock_data |
| NULL | TABLE | IX | GRANTED | NULL |
| PRIMARY | RECORD | X | GRANTED | 0 |
| PRIMARY | RECORD | X | GRANTED | 5 |
| PRIMARY | RECORD | X | GRANTED | 10 |
| PRIMARY | RECORD | X,GAP | GRANTED | 15 |
| id<=11 |
|---|
| index_name | lock_type | lock_mode | lock_status | lock_data |
| NULL | TABLE | IX | GRANTED | NULL |
| PRIMARY | RECORD | X | GRANTED | 0 |
| PRIMARY | RECORD | X | GRANTED | 5 |
| PRIMARY | RECORD | X | GRANTED | 10 |
| PRIMARY | RECORD | X,GAP | GRANTED | 15 |
论断：
X:next key lock，也就是 recordlock+ previous gap
x gap:previous gap
x rec not gap: rec
