Understand the concept of mysql_lock

For locks, you need to focus on the following:
  1. Lock classification
  ● Table locks
  ● Row locks
  ● Object locks (meta-table locks), implemented at the table cache layer
  ● Page locks
  ● Exclusive locks (mutexes, X locks)
  ● Shared locks ( S lock)

2. Precautions for the use of locks
  ● The innodb engine is a row-level lock, which is suitable for the background system of high concurrency scenarios
  ● The myisam engine uses a table-level lock, which is suitable for the front-end web system
  ● When delete\update is executed, it will be added by default Mutual exclusion lock
  ● innodb, if delete \update is not indexed in the field after the where condition, it will cause a lock table and serious concurrency performance
  ● When modifying fields, deleting primary key, and deleting primary key fields will cause meta-table locks

Set lock waiting timeout : innodb_lock_wait_timeout=500 (unit: s)
Commonly used commands for locks:
  ● View table lock contention
          show status like 'table%'
         

      The higher the value is, the more serious the lock contention is.

  ● Check the status of the lock table
          show processlist;
          the corresponding status value can see whether there is a lock table.