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现在很少使用原生jdbc去实现代码, 最近在测试MySQL批处理数据遇到一个问题: 执行Statement.executeBatch时效率极其低下(插入10000条数据), 断点调试时在此处停顿很长时间(908712ms)
数据版本:
select version(); // 5.7.17-11-V2.0R530D002-20190816-1203-log
数据库表:
CREATE TABLE `t_user` ( `id` int(11) NOT NULL AUTO_INCREMENT, `user_name` varchar(64) DEFAULT NULL, `age` smallint(6) DEFAULT NULL, `salary` decimal(10,2) DEFAULT NULL, `max_size` int(11) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=0 DEFAULT CHARSET=utf8;
测试代码如下:
public class BatchTest {
public static void main(String[] args) throws SQLException, ClassNotFoundException {
batch("com.mysql.cj.jdbc.Driver",
"jdbc:mysql://localhost:3306/test?serverTimezone=Asia/Shanghai&characterEncoding=utf8&useUnicode=true&useSSL=false&allowMultiQueries=true",
"root", "123456");
}
private static void batch(String driver, String url, String username, String password) throws ClassNotFoundException, SQLException {
// jdbc driver: mysql-connector-java:8.0.21
Class.forName(driver);
Connection conn = DriverManager.getConnection(url, username, password);
conn.setAutoCommit(false);
PreparedStatement pstmt = conn.prepareStatement("select * from dual");
for(int i = 1; i <= 10000; i++){
String batchSql = "insert into t_user(user_name, age, salary, max_size) values (" +
"'name" + i + "'," + i + "," + i + "," + i +
")";
pstmt.addBatch(batchSql);
}
long start = System.currentTimeMillis();
// 执行耗时很长
int[] rs = pstmt.executeBatch();
conn.commit();
// total ======> 908712
System.out.println("total ======> " + (System.currentTimeMillis() - start));
}
}原因
addBatch() 是在PreparedStatement定义的, addBatch(String) 是在Statement定义的，
MySQL JDBC驱动在默认情况下使用预编译会无视executeBatch()语句, 把我们期望批量执行的一组sql语句拆散, 一条一条地发给MySQL数据库, 直接造成较低的性能.
batchHasPlainStatements=true, 即使用PreparedStatement时使用了Statement.addBatch(String), 不执行批处理操作, 一条一条地发给MySQL数据库, 直接造成较低的性能.(确使用方式: PreparedStatement + addBatch(), Statement + addBatch(sql))
JDBC驱动源码:
public class ClientPreparedStatement extends com.mysql.cj.jdbc.StatementImpl implements JdbcPreparedStatement {
/**
* Does the batch (if any) contain "plain" statements added by
* Statement.addBatch(String)?
*
* If so, we can't re-write it to use multi-value or multi-queries.
*/
protected boolean batchHasPlainStatements = false;
// ......
protected long[] executeBatchInternal() throws SQLException {
synchronized (checkClosed().getConnectionMutex()) {
if (this.connection.isReadOnly()) {
throw new SQLException(Messages.getString("PreparedStatement.25") + Messages.getString("PreparedStatement.26"),
MysqlErrorNumbers.SQL_STATE_ILLEGAL_ARGUMENT);
}
if (this.query.getBatchedArgs() == null || this.query.getBatchedArgs().size() == 0) {
return new long[0];
}
// we timeout the entire batch, not individual statements
int batchTimeout = getTimeoutInMillis();
setTimeoutInMillis(0);
resetCancelledState();
try {
statementBegins();
clearWarnings();
// 1. batchHasPlainStatements 包含原始sql语句
// 2. rewriteBatchedStatements 使用批量
if (!this.batchHasPlainStatements && this.rewriteBatchedStatements.getValue()) {
if (((PreparedQuery) this.query).getParseInfo().canRewriteAsMultiValueInsertAtSqlLevel()) {
return executeBatchedInserts(batchTimeout);
}
if (!this.batchHasPlainStatements && this.query.getBatchedArgs() != null
&& this.query.getBatchedArgs().size() > 3 /* cost of option setting rt-wise */) {
return executePreparedBatchAsMultiStatement(batchTimeout);
}
}
return executeBatchSerially(batchTimeout);
} finally {
this.query.getStatementExecuting().set(false);
clearBatch();
}
}
}
// ......
}修正:
在连接url加上&rewriteBatchedStatements=true, 如: jdbc:mysql://localhost:3306/test?serverTimezone=Asia/Shanghai&characterEncoding=utf8&useUnicode=true&useSSL=false&allowMultiQueries=true&rewriteBatchedStatements=true
使用Statement.addBatch()替换Statement.addBatch(String)
public class BatchTest {
public static void main(String[] args) throws SQLException, ClassNotFoundException {
batch("com.mysql.cj.jdbc.Driver",
"jdbc:mysql://localhost:3306/test?serverTimezone=Asia/Shanghai&characterEncoding=utf8&useUnicode=true&useSSL=false&allowMultiQueries=true&rewriteBatchedStatements=true",
"root", "123456");
}
private static void batch(String driver, String url, String username, String password) throws ClassNotFoundException, SQLException {
Class.forName(driver);
Connection conn = DriverManager.getConnection(url, username, password);
conn.setAutoCommit(false);
String pSql = "insert into t_user(user_name, age, salary, max_size) values (?, ?, ?, ?)";
PreparedStatement pstmt =conn.prepareStatement(pSql);
for(int i = 1; i <= 10000; i++){
try {
pstmt.setString(1, "name" + i);
pstmt.setInt(2, i);
pstmt.setInt(3, i);
pstmt.setInt(4, i);
pstmt.addBatch();
} catch (SQLException e) {
e.printStackTrace();
}
}
long start = System.currentTimeMillis();
int[] rs = pstmt.executeBatch();
conn.commit();
// total ======> 2598
System.out.println("total ======> " + (System.currentTimeMillis() - start));
}
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