If you want to change a transaction data, others cannot change it while you change it.
So you need a lock, just like you go to an ATM to deposit money, this machine can only be used by you, and those who want to withdraw money are behind you. Cannot be used by everyone.
It is equivalent to the room you are visiting. As long as you go in, it must be locked for you to use. Only when you come out can others be locked.
This is called an exclusive lock. Exclusive lock
Back to the lock mechanism, the data that needs to be locked will be displayed in a selection table. Such a data record is locked by the selection table.
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Exclusive lock
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