MyBatis批量插入几千条数据，请慎用foreach

<insert id="batchInsert" parameterType="java.util.List">
    insert into USER (id, name) values
    <foreach collection="list" item="model" index="index" separator=","> 
        (#{model.id}, #{model.name})
    foreach>
insert>

这个方法提升批量插入速度的原理是，将传统的：

INSERT INTO `table1` (`field1`, `field2`) VALUES ("data1", "data2");
INSERT INTO `table1` (`field1`, `field2`) VALUES ("data1", "data2");
INSERT INTO `table1` (`field1`, `field2`) VALUES ("data1", "data2");
INSERT INTO `table1` (`field1`, `field2`) VALUES ("data1", "data2");
INSERT INTO `table1` (`field1`, `field2`) VALUES ("data1", "data2");

转化为：搜索公众号互联网架构师回复“2T”，送你一份惊喜礼包。

INSERT INTO `table1` (`field1`, `field2`) 
VALUES ("data1", "data2"),
("data1", "data2"),
("data1", "data2"),
("data1", "data2"),
("data1", "data2");

Of course don't combine ALL of them, if the amount is HUGE. Say you have 1000 rows you need to insert, then don't do it one at a time. You shouldn't equally try to have all 1000 rows in a single query. Instead break it into smaller sizes.

Insert inside Mybatis foreach is not batch, this is a single (could become giant) SQL statement and that brings drawbacks:

• some database such as Oracle here does not support.

• in relevant cases: there will be a large number of records to insert and the database configured limit (by default around 2000 parameters per statement) will be hit, and eventually possibly DB stack error if the statement itself become too large.

Iteration over the collection must not be done in the mybatis XML. Just execute a simple Insertstatement in a Java Foreach loop. The most important thing is the session Executor type.

SqlSession session = sessionFactory.openSession(ExecutorType.BATCH);
for (Model model : list) {
    session.insert("insertStatement", model);
}
session.flushStatements();

Internally, it still generates the same single insert statement with many placeholders as the JDBC code above.

MyBatis has an ability to cache PreparedStatement, but this statement cannot be cached because it contains  element and the statement varies depending on the parameters. As a result, MyBatis has to 1) evaluate the foreach part and 2) parse the statement string to build parameter mapping [1] on every execution of this statement.

And these steps are relatively costly process when the statement string is big and contains many placeholders.

[1] simply put, it is a mapping between placeholders and the parameters.

SqlSession session = sqlSessionFactory.openSession(ExecutorType.BATCH);
try {
    SimpleTableMapper mapper = session.getMapper(SimpleTableMapper.class);
    List records = getRecordsToInsert(); // not shown
 
    BatchInsert batchInsert = insert(records)
            .into(simpleTable)
            .map(id).toProperty("id")
            .map(firstName).toProperty("firstName")
            .map(lastName).toProperty("lastName")
            .map(birthDate).toProperty("birthDate")
            .map(employed).toProperty("employed")
            .map(occupation).toProperty("occupation")
            .build()
            .render(RenderingStrategy.MYBATIS3);
 
    batchInsert.insertStatements().stream().forEach(mapper::insert);
 
    session.commit();
} finally {
    session.close();
}

Connection connection = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/mydb?useUnicode=true&characterEncoding=UTF-8&useServerPrepStmts=false&rewriteBatchedStatements=true","root","root");
connection.setAutoCommit(false);
PreparedStatement ps = connection.prepareStatement(
        "insert into tb_user (name) values(?)");
for (int i = 0; i < stuNum; i++) {
    ps.setString(1,name);
    ps.addBatch();
}
ps.executeBatch();
connection.commit();
connection.close();

1. https://dev.mysql.com/doc/refman/5.6/en/insert-optimization.html

2. https://stackoverflow.com/questions/19682414/how-can-mysql-insert-millions-records-fast
3. https://stackoverflow.com/questions/32649759/using-foreach-to-do-batch-insert-with-mybatis/40608353
4. https://blog.csdn.net/wlwlwlwl015/article/details/50246717
5. http://blog.harawata.net/2016/04/bulk-insert-multi-row-vs-batch-using.html
6. https://www.red-gate.com/simple-talk/sql/performance/comparing-multiple-rows-insert-vs-single-row-insert-with-three-data-load-methods/
7. https://stackoverflow.com/questions/7004390/java-batch-insert-into-mysql-very-slow
8. http://www.mybatis.org/mybatis-dynamic-sql/docs/insert.html

全栈架构社区交流群