类 MySQLMaxValueIncrementer

public class MySQLMaxValueIncrementer
extends AbstractColumnMaxValueIncrementer

DataFieldMaxValueIncrementer that increments the maximum value of a given MySQL table with the equivalent of an auto-increment column. Note: If you use this class, your MySQL key column should NOT be auto-increment, as the sequence table does the job.

The sequence is kept in a table; there should be one sequence table per table that needs an auto-generated key. The storage engine used by the sequence table can be MYISAM or INNODB since the sequences are allocated using a separate connection without being affected by any other transactions that might be in progress.

Example:

create table tab (id int unsigned not null primary key, text varchar(100));
 create table tab_sequence (value int not null);
 insert into tab_sequence values(0);

If "cacheSize" is set, the intermediate values are served without querying the database. If the server or your application is stopped or crashes or a transaction is rolled back, the unused values will never be served. The maximum hole size in numbering is consequently the value of cacheSize.

It is possible to avoid acquiring a new connection for the incrementer by setting the "useNewConnection" property to false. In this case you MUST use a non-transactional storage engine like MYISAM when defining the incrementer table.