MyBatis批量插入幾千條數(shù)據(jù)，請(qǐng)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>

這個(gè)方法提升批量插入速度的原理是，將傳統(tǒng)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");

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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?????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

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