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2025-01-18 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > Database >
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Shulou(Shulou.com)06/01 Report--
1. Type
Exclusive locks: record, row level
Shared locks: table level, preventing table structure from being modified using DDL
Shared lock [S lock]
Also known as read lock, if transaction T adds an S lock to the data object A, transaction T can read A but cannot modify A. other transactions can only add S lock to An instead of X lock until T releases the S lock on A. This ensures that other transactions can read A, but no modifications can be made to A until T releases the S lock on A.
Exclusive lock [X lock]
Also known as write lock. If transaction T adds an X lock to the data object A, transaction T can read An or modify A, and other transactions can no longer lock A until T releases the lock on A. This ensures that other transactions cannot read and modify A until T releases the lock on A.
2 、 select for update
Select * from emp for update; returns the result after waiting for row lock to be released
Manual lock protection to lock only specified row records
Select for update nowait returns an error if it is locked
3. Deadlock
Popular explanation: an is waiting for the resource release of B, and B is waiting for the resource release of A.
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