使用mysql提供sequence的服务，我们在执行的一个方案：

1：创建sequence相关表

CREATE TABLE `seq_order_id` (  `seq` bigint(20) NOT NULL AUTO_INCREMENT,  `stub` varchar(3) NOT NULL,  PRIMARY KEY (`seq`),  UNIQUE KEY `stub` (`stub`)) ENGINE=InnoDB AUTO_INCREMENT=10000 DEFAULT CHARSET=utf8;

2：获取seq时相关SQL：

REPLACE INTO seq_order_id(stub) VALUES (#stub#)SELECT last_insert_id()

这种方式可以一个表提供给多个业务做seq的服务，但是由于REPLACE INTO会有锁表状况存在，在业务量很大时，对数据库的性能影响较大。

3：修改为使用spring的org.springframework.jdbc.support.incrementer.MySQLMaxValueIncrementer，方法加了同步锁，每次数据库操作会直接获取一个段的值cacheSize，业务分布式部署也不影响sequence的唯一性

@Override	protected synchronized long getNextKey() throws DataAccessException {		if (this.maxId == this.nextId) {			/*			* Need to use straight JDBC code because we need to make sure that the insert and select			* are performed on the same connection (otherwise we can't be sure that last_insert_id()			* returned the correct value)			*/			Connection con = DataSourceUtils.getConnection(getDataSource());			Statement stmt = null;			try {				stmt = con.createStatement();				DataSourceUtils.applyTransactionTimeout(stmt, getDataSource());				// Increment the sequence column...				String columnName = getColumnName();				stmt.executeUpdate("update "+ getIncrementerName() + " set " + columnName +						" = last_insert_id(" + columnName + " + " + getCacheSize() + ")");				// Retrieve the new max of the sequence column...				ResultSet rs = stmt.executeQuery(VALUE_SQL);				try {					if (!rs.next()) {						throw new DataAccessResourceFailureException("last_insert_id() failed after executing an update");					}					this.maxId = rs.getLong(1);				}				finally {					JdbcUtils.closeResultSet(rs);				}				this.nextId = this.maxId - getCacheSize() + 1;			}			catch (SQLException ex) {				throw new DataAccessResourceFailureException("Could not obtain last_insert_id()", ex);			}			finally {				JdbcUtils.closeStatement(stmt);				DataSourceUtils.releaseConnection(con, getDataSource());			}		}		else {			this.nextId++;		}		return this.nextId;	}