MySQL intent lock

An intent lock indicates that a transaction is locking a row or is about to lock a row , Show an intention . It is divided into intentional shared locks （IS） And intent exclusive lock （IX）：

Before a transaction adds a shared lock to a row of a table , You must get a IS Lock or lock with higher priority .
A transaction adds an exclusive lock to a row of a table , It must get a IX lock .
Intention lock belongs to table lock , It doesn't work with innodb Row lock conflict in , There will be no conflict between any two intention locks , But it will be locked with the watch （S Lock and X lock ） Conflict , The following table ：

Compatibility     S lock     X lock
IS lock      compatible      Conflict
IX lock      Conflict      Conflict
Table locks and row locks have ensured the isolation of transactions , Make sure the data is consistent , So why use intent lock ？
Intentional locking plays a role when a transaction is locked with a table . For example, a transaction wants to lock the table exclusively , If there is no intention to lock , Before locking, the transaction needs to judge whether each row of the current table has been locked , If the watch is big , It takes a lot of time to traverse each row for judgment . If intention lock is used , Then before locking the watch , Just judge whether the current table has intention lock , This speeds up the processing of table locks .
Intentional locks are maintained by the storage engine itself , Internal mechanism , The user cannot operate the intention lock .