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     最近在做一个银行的生产数据脱敏系统，今天写代码时遇到了一个“瓶颈”，脱敏系统需要将生产环境上Infoxmix里的数据原封不动的Copy到另一台Oracle数据库服务器上，然后对Copy后的数据作些漂白处理。为了将人为干预的因素降到最低，在系统设计时采用Java代码对数据作Copy,思路如图

    首先在代码与生产库间建立一个Connection，将读取到的数据放在ResultSet对象，然后再与开发库建立一个Connection。从ResultSet取出数据后通过TestConnection插入到开发库，以此来实现Copy。代码写完后运行程序，速度太慢了，一秒钟只能Copy一千条数据，生产库上有上亿条数据，按照这个速度同步完要到猴年马月呀,用PreparedStatement批处理速度也没有提交多少。我想能不能用多线程处理，多个人干活总比一个人干活速度要快。

    假设生产库有1万条数据，我开5个线程，每个线程分2000条数据，同时向开发库里插数据，Oracle支持高并发这样的话速度至少会提高好多倍，按照这个思路重新进行了编码，批处理设置为1万条一提交，统计插入数量的变量使用java.util.concurrent.atomic.AtomicLong，程序一运行，传输速度飞快CPU利用率在70%~90%，现在一秒钟可以拷贝50万条记录，没过几分钟上亿条数据一条不落地全部Copy到目标库。

在查询的时候我用了如下语句

String queryStr = "SELECT * FROM xx";

ResultSet coreRs = PreparedStatement.executeQuery(queryStr);

实习生问如果xx表里有上千万条记录，你全部查询出来放到ResultSet,那内存不溢出了么？Java在设计的时候已经考虑到这个问题了，并没有查询出所有的数据，而是只查询了一部分数据放到ResultSet,数据“用完”它会自动查询下一批数据，你可以用setFetchSize(int rows)方法设置一个建议值给ResultSet,告诉它每次从数据库Fetch多少条数据。但我不赞成，因为JDBC驱动会根据实际情况自动调整Fetch的数量。另外性能也与网线的带宽有直接的关系。

相关代码

package com.dlbank.domain;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.Statement;import java.util.List;import java.util.concurrent.atomic.AtomicLong;import org.apache.log4j.Logger;/** *
title: 数据同步类 
   *
Description: 该类用于将生产核心库数据同步到开发库
   *@author Tank Zhang  */public class CoreDataSyncImpl implements CoreDataSync {		private List
   
     coreTBNames; //要同步的核心库表名	private ConnectionFactory connectionFactory;	private Logger log = Logger.getLogger(getClass());		private AtomicLong currentSynCount = new AtomicLong(0L); //当前已同步的条数		private int syncThreadNum;  //同步的线程数	@Override	public void syncData(int businessType) throws Exception {				for (String tmpTBName : coreTBNames) {			log.info("开始同步核心库" + tmpTBName + "表数据");			// 获得核心库连接			Connection coreConnection = connectionFactory.getDMSConnection(4);			Statement coreStmt = coreConnection.createStatement();			//为每个线程分配结果集			ResultSet coreRs = coreStmt.executeQuery("SELECT count(*) FROM "+tmpTBName);			coreRs.next();			//总共处理的数量			long totalNum = coreRs.getLong(1);			//每个线程处理的数量			long ownerRecordNum =(long) Math.ceil((totalNum / syncThreadNum)); 			log.info("共需要同步的数据量："+totalNum);			log.info("同步线程数量："+syncThreadNum);			log.info("每个线程可处理的数量："+ownerRecordNum);			// 开启五个线程向目标库同步数据			for(int i=0; i < syncThreadNum; i ++){				StringBuilder sqlBuilder = new StringBuilder();				//拼装后SQL示例				//Select * From dms_core_ds Where id between 1 And 657398				//Select * From dms_core_ds Where id between 657399 And 1314796				//Select * From dms_core_ds Where id between 1314797 And 1972194				//Select * From dms_core_ds Where id between 1972195 And 2629592				//Select * From dms_core_ds Where id between 2629593 And 3286990				//..				sqlBuilder.append("Select * From ").append(tmpTBName)						.append(" Where id between " ).append(i * ownerRecordNum +1)						.append( " And ")						.append((i * ownerRecordNum + ownerRecordNum));				Thread workThread = new Thread(						new WorkerHandler(sqlBuilder.toString(),businessType,tmpTBName));				workThread.setName("SyncThread-"+i);				workThread.start();			}			while (currentSynCount.get() < totalNum);			//休眠一会儿让数据库有机会commit剩余的批处理(只针对JUnit单元测试,因为单元测试完成后会关闭虚拟器，使线程里的代码没有机会作提交操作);			//Thread.sleep(1000 * 3);			log.info( "核心库"+tmpTBName+"表数据同步完成，共同步了" + currentSynCount.get() + "条数据");		}	}// end for loop		public void setCoreTBNames(List
    
      coreTBNames) {		this.coreTBNames = coreTBNames;	}	public void setConnectionFactory(ConnectionFactory connectionFactory) {		this.connectionFactory = connectionFactory;	}		public void setSyncThreadNum(int syncThreadNum) {		this.syncThreadNum = syncThreadNum;	}		//数据同步线程	final class WorkerHandler implements Runnable {		ResultSet coreRs;		String queryStr;		int businessType;		String targetTBName;		public WorkerHandler(String queryStr,int businessType,String targetTBName) {			this.queryStr = queryStr;			this.businessType = businessType;			this.targetTBName = targetTBName;		}		@Override		public void run() {			try {				//开始同步				launchSyncData();			} catch(Exception e){				log.error(e);				e.printStackTrace();			}		}		//同步数据方法		void launchSyncData() throws Exception{			// 获得核心库连接			Connection coreConnection = connectionFactory.getDMSConnection(4);			Statement coreStmt = coreConnection.createStatement();			// 获得目标库连接			Connection targetConn = connectionFactory.getDMSConnection(businessType);			targetConn.setAutoCommit(false);// 设置手动提交			PreparedStatement targetPstmt = targetConn.prepareStatement("INSERT INTO " + targetTBName+" VALUES (?,?,?,?,?)");			ResultSet coreRs = coreStmt.executeQuery(queryStr);			log.info(Thread.currentThread().getName()+"'s Query SQL::"+queryStr);			int batchCounter = 0; //累加的批处理数量			while (coreRs.next()) {				targetPstmt.setString(1, coreRs.getString(2));				targetPstmt.setString(2, coreRs.getString(3));				targetPstmt.setString(3, coreRs.getString(4));				targetPstmt.setString(4, coreRs.getString(5));				targetPstmt.setString(5, coreRs.getString(6));				targetPstmt.addBatch();				batchCounter++;				currentSynCount.incrementAndGet();//递增				if (batchCounter % 10000 == 0) { //1万条数据一提交					targetPstmt.executeBatch();					targetPstmt.clearBatch();					targetConn.commit();				}			}			//提交剩余的批处理			targetPstmt.executeBatch();			targetPstmt.clearBatch();			targetConn.commit();			//释放连接 			connectionFactory.release(targetConn, targetPstmt,coreRs);		}	}}
    
   

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