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MySQL 5.7 Reference Manual  /  ...  /  Performing DML and DDL Statements on the Underlying InnoDB Table

14.17.5.6 Performing DML and DDL Statements on the Underlying InnoDB Table

You can access the InnoDB table (by default, test.demo_test) through the standard SQL interfaces. However, there are some restrictions:

  • When query a table through SQL that is also being accessed through the memcached interface, remember that memcached operations can be configured to be committed periodically rather than after every write operation. This behavior is controlled by the daemon_memcached_w_batch_size option. If this option is set to a value greater than 1, use READ UNCOMMITTED queries to find the just-inserted rows:

    
    mysql> set session TRANSACTION ISOLATION LEVEL read uncommitted;
    Query OK, 0 rows affected (0.00 sec)
    
    mysql> select * from demo_test;
    +------+------+------+------+-----------+------+------+------+------+------+------+
    | cx   | cy   | c1   | cz   | c2        | ca   | CB   | c3   | cu   | c4   | C5   |
    +------+------+------+------+-----------+------+------+------+------+------+------+
    | NULL | NULL | a11  | NULL | 123456789 | NULL | NULL |   10 | NULL |    3 | NULL |
    +------+------+------+------+-----------+------+------+------+------+------+------+
    1 row in set (0.00 sec)
    
    
  • When modifying a table using SQL that is also accessed through the memcached interface, you can configure memcached operations to start a new transaction periodically rather than for every read operation. This behavior is controlled by the daemon_memcached_r_batch_size option. If this option is set to a value greater than 1, changes made to the table using SQL are not immediately visible to memcached operations.

  • The InnoDB table is locked IS (shared intention) or IX (exclusive intentional) for all operations in a transaction. If you increase daemon_memcached_r_batch_size and daemon_memcached_w_batch_size substantially from their default value of 1, the table is most likely intentionally locked between each operation, preventing you from running DDL statements on the table.


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