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关于rewriteBatchedStatements的源码分析

news 2025/8/5 9:19:25

在之前的优惠券兑换码需求中，涉及批量写入问题，其中有一个关键的连接配置参数非常重要——rewriteBatchedStatements，当该值配置为true时，Statement将可能对批量插入sql进行重写。

何谓重写？原来提交的批量执行语句（100条）如下：

INSERT INTO dh_redeem_code (code, status, coupon_id, batch_id) VALUES ('1','0',100,1);
INSERT INTO dh_redeem_code (code, status, coupon_id, batch_id) VALUES ('2','0',100,1);
...
INSERT INTO dh_redeem_code (code, status, coupon_id, batch_id) VALUES ('100','0',100,1);

重写之后的sql语句（1条）如下：

INSERT INTO dh_redeem_code (code, status, coupon_id, batch_id) VALUES 
('1','0',100,1),
('2','0',100,1),
...
('100','0',100,1);

本文将从源码层面来对该参数的作用进行分析。笔者采用的mysql数据库驱动依赖库为mysql-connector-java:8.0.30。

首先，我们来看一段ClientPreparedStatement.executeBatchInternal()方法的代码，这是数据库驱动内部执行批量sql的方法。

if (!this.batchHasPlainStatements && this.rewriteBatchedStatements.getValue()) {if (getQueryInfo().isRewritableWithMultiValuesClause()) {return executeBatchWithMultiValuesClause(batchTimeout);}if (!this.batchHasPlainStatements && this.query.getBatchedArgs() != null&& this.query.getBatchedArgs().size() > 3 /* cost of option setting rt-wise */) {return executePreparedBatchAsMultiStatement(batchTimeout);}
}

关于batchHasPlainStatements属性，如果批处理使用 Statement.addBatch（String）显示添加sql语句，则该属性值为true，否则为false。原文如下：

/*** 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;

第一行代码的意思：如果没有使用 Statement.addBatch（String）显示添加sql语句，并且rewriteBatchedStatements参数值为true，则有可能对批量语句进行重写。

继续往下看，isRewritableWithMultiValuesClause这个属性值为true，则执行executeBatchWithMultiValuesClause方法，该方法实现对sql语句的重写。

对于isRewritableWithMultiValuesClause属性的赋值，QueryInfo类的构造函数中

public QueryInfo(String sql, Session session, String encoding) {// Check if the statement has potential to be rewritten as a multi-values clause statement, i.e., if it is an INSERT or REPLACE statement and// 'rewriteBatchedStatements' is enabled.boolean rewritableAsMultiValues = (isInsert || isReplace) && rewriteBatchedStatements;...        //这里有很长很长很长一段代码this.isRewritableWithMultiValuesClause = rewritableAsMultiValues;
}

从第4行代码看出重写的必要条件：rewriteBatchedStatements值为true，而且必须是插入操作或者REPLACE操作。

再来看看sql语句重写函数executeBatchWithMultiValuesClause(batchTimeout)代码：

batchedStatement = /* FIXME -if we ever care about folks proxying our JdbcConnection */prepareBatchedInsertSQL(locallyScopedConn, numValuesPerBatch);timeoutTask = startQueryTimer(batchedStatement, batchTimeout);numberToExecuteAsMultiValue = numBatchedArgs < numValuesPerBatch ? numBatchedArgs : numBatchedArgs / numValuesPerBatch;int numberArgsToExecute = numberToExecuteAsMultiValue * numValuesPerBatch;for (int i = 0; i < numberArgsToExecute; i++) {if (i != 0 && i % numValuesPerBatch == 0) {try {updateCountRunningTotal += batchedStatement.executeLargeUpdate();} catch (SQLException ex) {sqlEx = handleExceptionForBatch(batchCounter - 1, numValuesPerBatch, updateCounts, ex);}getBatchedGeneratedKeys(batchedStatement);batchedStatement.clearParameters();batchedParamIndex = 1;}batchedParamIndex = setOneBatchedParameterSet(batchedStatement, batchedParamIndex, this.query.getBatchedArgs().get(batchCounter++));
}try {updateCountRunningTotal += batchedStatement.executeLargeUpdate();
} catch (SQLException ex) {sqlEx = handleExceptionForBatch(batchCounter - 1, numValuesPerBatch, updateCounts, ex);
}getBatchedGeneratedKeys(batchedStatement);

上述代码第一行将根据批量sql数量和插入的字段数量，构建带有占位符的sql。随后的语句遍历批量sql，使用实际的插入参数值替换占位符，从而形成一条可执行的批量插入语句。

自此，关于rewriteBatchedStatements的源码分析结束，如果需要数据库驱动重写批量插入，只需要正常使用MybatisPlus的saveBatch方法，并在数据库连接中加上rewriteBatchedStatements=true的配置信息即可。

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