When to use InnoDB to set index records?
If a secondary index is used in a search and the index record locks to be set are exclusive, InnoDB also retrieves the corresponding clustered index records and sets locks on them.
What’s the difference between lock tables and InnoDB?
InnoDB also sets these locks in the case where the constraint fails. LOCK TABLES sets table locks, but it is the higher MySQL layer above the InnoDB layer that sets these locks. InnoDB is aware of table locks if innodb_table_locks = 1 (the default) and autocommit = 0, and the MySQL layer above InnoDB knows about row-level locks.
How does InnoDB fetch auto increment without setting locks?
InnoDB fetches the value of a previously initialized AUTO_INCREMENT column without setting any locks. If a FOREIGN KEY constraint is defined on a table, any insert, update, or delete that requires the constraint condition to be checked sets shared record-level locks on the records that it looks at to check the constraint.
What are the different types of lock in InnoDB?
InnoDB sets specific types of locks as follows. SELECT FROM is a consistent read, reading a snapshot of the database and setting no locks unless the transaction isolation level is set to SERIALIZABLE. For SERIALIZABLE level, the search sets shared next-key locks on the index records it encounters.
How are locks set in MySQL 5.7 reference manual?
A locking read, an UPDATE, or a DELETE generally set record locks on every index record that is scanned in the processing of the SQL statement. It does not matter whether there are WHERE conditions in the statement that would exclude the row. InnoDB does not remember the exact WHERE condition, but only knows which index ranges were scanned.
How to set lock in share mode in MySQL?
LOCK IN SHARE MODE sets shared next-key locks on all index records the search encounters. However, only an index record lock is required for statements that lock rows using a unique index to search for a unique row. SELECT FOR UPDATE sets an exclusive next-key lock on every record the search encounters.