二级缓存问题
情形一：
@Test
public void testLv2Cache(){
SqlSession sqlSession=null;
try {
sqlSession = MyBatisUtils.openSession();
Goods goods = sqlSession.selectOne("goods.selectById", 2648);
Goods goods2 = new Goods();
goods2.setTitle("测试标题aaaaa");
goods2.setSubTitle("测试副标题bbbbb");
goods2.setOriginalCost(200f);
goods2.setCurrentPrice(400f);
goods2.setDiscount(0.5f);
goods2.setIsFreeDelivery(1);
goods2.setCategoryId(43);
sqlSession.insert("goods.insertGoods",goods2);
Goods goods1 = sqlSession.selectOne("goods.selectById", 2648);
System.out.println(goods.hashCode()+":"+ goods);
System.out.println(goods1.hashCode()+":"+goods1);
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
MyBatisUtils.closeSession(sqlSession);
}
System.out.println("-----------------------------------");
try {
sqlSession = MyBatisUtils.openSession();
Goods goods = sqlSession.selectOne("goods.selectById", 2648);
Goods goods1 = sqlSession.selectOne("goods.selectById", 2648);
System.out.println(goods.hashCode()+":"+ goods);
System.out.println(goods1.hashCode()+":"+goods1);
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
MyBatisUtils.closeSession(sqlSession);
}
System.out.println("-----------------------------------");
try {
sqlSession = MyBatisUtils.openSession();
Goods goods = sqlSession.selectOne("goods.selectById", 2648);
Goods goods1 = sqlSession.selectOne("goods.selectById", 2648);
System.out.println(goods.hashCode()+":"+ goods);
System.out.println(goods1.hashCode()+":"+goods1);
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
MyBatisUtils.closeSession(sqlSession);
}
}情形一的测试结果：
LoggingCache:60 =>[DEBUG] Cache Hit Ratio [goods]: 0.0 JdbcTransaction:143 =>[DEBUG] Opening JDBC Connection JdbcTransaction:107 =>[DEBUG] Setting autocommit to false on JDBC Connection [com.alibaba.druid.pool.DruidStatementConnection@40db2a24] BaseJdbcLogger:135 =>[DEBUG] ==> Preparing: select * from t_goods where goods_id = ? BaseJdbcLogger:135 =>[DEBUG] ==> Parameters: 2648(Integer) BaseJdbcLogger:135 =>[DEBUG] <== Total: 1 BaseJdbcLogger:135 =>[DEBUG] ==> Preparing: insert into t_goods(title,sub_title,original_cost,current_price,discount,is_free_delivery,category_id) values(?,?,?,?,?,?,?) BaseJdbcLogger:135 =>[DEBUG] ==> Parameters: 测试标题aaaaa(String), 测试副标题bbbbb(String), 200.0(Float), 400.0(Float), 0.5(Float), 1(Integer), 43(Integer) BaseJdbcLogger:135 =>[DEBUG] <== Updates: 1 BaseJdbcLogger:135 =>[DEBUG] ==> Preparing: select last_insert_id() BaseJdbcLogger:135 =>[DEBUG] ==> Parameters: BaseJdbcLogger:135 =>[DEBUG] <== Total: 1 LoggingCache:60 =>[DEBUG] Cache Hit Ratio [goods]: 0.0 BaseJdbcLogger:135 =>[DEBUG] ==> Preparing: select * from t_goods where goods_id = ? BaseJdbcLogger:135 =>[DEBUG] ==> Parameters: 2648(Integer) BaseJdbcLogger:135 =>[DEBUG] <== Total: 1 680988889:新安怡新生宝宝沐浴露200毫升 SCF981/02 1511574902:新安怡新生宝宝沐浴露200毫升 SCF981/02 JdbcTransaction:86 =>[DEBUG] Rolling back JDBC Connection [com.alibaba.druid.pool.DruidStatementConnection@40db2a24] JdbcTransaction:130 =>[DEBUG] Resetting autocommit to true on JDBC Connection [com.alibaba.druid.pool.DruidStatementConnection@40db2a24] JdbcTransaction:97 =>[DEBUG] Closing JDBC Connection [com.alibaba.druid.pool.DruidStatementConnection@40db2a24] ----------------------------------- LoggingCache:60 =>[DEBUG] Cache Hit Ratio [goods]: 0.0 JdbcTransaction:143 =>[DEBUG] Opening JDBC Connection JdbcTransaction:107 =>[DEBUG] Setting autocommit to false on JDBC Connection [com.alibaba.druid.pool.DruidStatementConnection@40db2a24] BaseJdbcLogger:135 =>[DEBUG] ==> Preparing: select * from t_goods where goods_id = ? BaseJdbcLogger:135 =>[DEBUG] ==> Parameters: 2648(Integer) BaseJdbcLogger:135 =>[DEBUG] <== Total: 1 LoggingCache:60 =>[DEBUG] Cache Hit Ratio [goods]: 0.0 1077873186:新安怡新生宝宝沐浴露200毫升 SCF981/02 1077873186:新安怡新生宝宝沐浴露200毫升 SCF981/02 JdbcTransaction:130 =>[DEBUG] Resetting autocommit to true on JDBC Connection [com.alibaba.druid.pool.DruidStatementConnection@40db2a24] JdbcTransaction:97 =>[DEBUG] Closing JDBC Connection [com.alibaba.druid.pool.DruidStatementConnection@40db2a24] ----------------------------------- LoggingCache:60 =>[DEBUG] Cache Hit Ratio [goods]: 0.2 LoggingCache:60 =>[DEBUG] Cache Hit Ratio [goods]: 0.3333333333333333 1077873186:新安怡新生宝宝沐浴露200毫升 SCF981/02 1077873186:新安怡新生宝宝沐浴露200毫升 SCF981/02
情形二：
@Test
public void testLv2Cache(){
SqlSession sqlSession=null;
try {
sqlSession = MyBatisUtils.openSession();
Goods goods = sqlSession.selectOne("goods.selectById", 2648);
Goods goods1 = sqlSession.selectOne("goods.selectById", 2648);
System.out.println(goods.hashCode()+":"+ goods.getTitle());
System.out.println(goods1.hashCode()+":"+goods1.getTitle());
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
MyBatisUtils.closeSession(sqlSession);
}
System.out.println("-----------------------------------");
try {
sqlSession = MyBatisUtils.openSession();
Goods goods = sqlSession.selectOne("goods.selectById", 2648);
Goods goods2 = new Goods();
goods2.setTitle("测试标题aaaaa");
goods2.setSubTitle("测试副标题bbbbb");
goods2.setOriginalCost(200f);
goods2.setCurrentPrice(400f);
goods2.setDiscount(0.5f);
goods2.setIsFreeDelivery(1);
goods2.setCategoryId(43);
sqlSession.insert("goods.insertGoods",goods2);
Goods goods1 = sqlSession.selectOne("goods.selectById", 2648);
System.out.println(goods.hashCode()+":"+ goods.getTitle());
System.out.println(goods1.hashCode()+":"+goods1.getTitle());
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
MyBatisUtils.closeSession(sqlSession);
}
System.out.println("-----------------------------------");
try {
sqlSession = MyBatisUtils.openSession();
Goods goods = sqlSession.selectOne("goods.selectById", 2648);
Goods goods1 = sqlSession.selectOne("goods.selectById", 2648);
System.out.println(goods.hashCode()+":"+ goods.getTitle());
System.out.println(goods1.hashCode()+":"+goods1.getTitle());
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
MyBatisUtils.closeSession(sqlSession);
}
}情形二的测试结果：
DruidDataSource:1002 =>[INFO] {dataSource-1} inited
LoggingCache:60 =>[DEBUG] Cache Hit Ratio [goods]: 0.0
JdbcTransaction:143 =>[DEBUG] Opening JDBC Connection
JdbcTransaction:107 =>[DEBUG] Setting autocommit to false on JDBC Connection [com.alibaba.druid.pool.DruidStatementConnection@40db2a24]
BaseJdbcLogger:135 =>[DEBUG] ==> Preparing: select * from t_goods where goods_id = ?
BaseJdbcLogger:135 =>[DEBUG] ==> Parameters: 2648(Integer)
BaseJdbcLogger:135 =>[DEBUG] <== Total: 1
LoggingCache:60 =>[DEBUG] Cache Hit Ratio [goods]: 0.0
1783966110:新安怡新生宝宝沐浴露200毫升 SCF981/02
1783966110:新安怡新生宝宝沐浴露200毫升 SCF981/02
JdbcTransaction:130 =>[DEBUG] Resetting autocommit to true on JDBC Connection [com.alibaba.druid.pool.DruidStatementConnection@40db2a24]
JdbcTransaction:97 =>[DEBUG] Closing JDBC Connection [com.alibaba.druid.pool.DruidStatementConnection@40db2a24]
-----------------------------------
LoggingCache:60 =>[DEBUG] Cache Hit Ratio [goods]: 0.3333333333333333
JdbcTransaction:143 =>[DEBUG] Opening JDBC Connection
JdbcTransaction:107 =>[DEBUG] Setting autocommit to false on JDBC Connection [com.alibaba.druid.pool.DruidStatementConnection@40db2a24]
BaseJdbcLogger:135 =>[DEBUG] ==> Preparing: insert into t_goods(title,sub_title,original_cost,current_price,discount,is_free_delivery,category_id) values(?,?,?,?,?,?,?)
BaseJdbcLogger:135 =>[DEBUG] ==> Parameters: 测试标题aaaaa(String), 测试副标题bbbbb(String), 200.0(Float), 400.0(Float), 0.5(Float), 1(Integer), 43(Integer)
BaseJdbcLogger:135 =>[DEBUG] <== Updates: 1
BaseJdbcLogger:135 =>[DEBUG] ==> Preparing: select last_insert_id()
BaseJdbcLogger:135 =>[DEBUG] ==> Parameters:
BaseJdbcLogger:135 =>[DEBUG] <== Total: 1
LoggingCache:60 =>[DEBUG] Cache Hit Ratio [goods]: 0.5
BaseJdbcLogger:135 =>[DEBUG] ==> Preparing: select * from t_goods where goods_id = ?
BaseJdbcLogger:135 =>[DEBUG] ==> Parameters: 2648(Integer)
BaseJdbcLogger:135 =>[DEBUG] <== Total: 1
1783966110:新安怡新生宝宝沐浴露200毫升 SCF981/02
1511574902:新安怡新生宝宝沐浴露200毫升 SCF981/02
JdbcTransaction:86 =>[DEBUG] Rolling back JDBC Connection [com.alibaba.druid.pool.DruidStatementConnection@40db2a24]
JdbcTransaction:130 =>[DEBUG] Resetting autocommit to true on JDBC Connection [com.alibaba.druid.pool.DruidStatementConnection@40db2a24]
JdbcTransaction:97 =>[DEBUG] Closing JDBC Connection [com.alibaba.druid.pool.DruidStatementConnection@40db2a24]
-----------------------------------
LoggingCache:60 =>[DEBUG] Cache Hit Ratio [goods]: 0.6
LoggingCache:60 =>[DEBUG] Cache Hit Ratio [goods]: 0.6666666666666666
1783966110:新安怡新生宝宝沐浴露200毫升 SCF981/02
1783966110:新安怡新生宝宝沐浴露200毫升 SCF981/02说明：默认开启了一级缓存，手动开启了二级缓存
相同点：情形1和情形2中都含有三段相同代码
不同点：
情形1在第一段代码查询中间插入了insert()不提交
情形2在第二段代码查询中间插入了insert()不提交
问题：
情形1哈希码 —— a b c c c c
680988889 （a）
1511574902 （b）
-------------
1077873186 （c）
1077873186 （c）
-------------
1077873186 （c）
1077873186 （c）
情形2哈希码 —— a a a b a a
1783966110 （a）
1783966110 （a）
--------------
1783966110 （a）
1511574902 （b）
--------------
1783966110 （a）
1783966110 （a）
情形1和情形2无法自圆其说，因为都开启了一级缓存和二级缓存，请解释？谢谢
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1回答
同学你好，1、在MyBatis中，开启了二级缓存并且在代码中插入了一个不提交的insert操作时，这确实会对一级缓存和二级缓存产生干扰，尤其是当这些操作在同一个SqlSession中执行时。
2、下面是对这种情形的详细分析：
1)一级缓存（SqlSession级别）:
当执行第一次查询时，MyBatis会查询数据库并将结果放入一级缓存。
接下来，执行了一个insert操作来插入一个新的商品记录（goods2）。由于这个insert操作没有提交（即没有调用sqlSession.commit()），这个变更在数据库中是看不到的，但它会清空一级缓存，因为MyBatis认为数据可能已经发生了改变。
由于一级缓存已被清空，当您再次执行相同的查询时，MyBatis不会从一级缓存中获取结果，而是会再次查询数据库。
2)二级缓存（Mapper级别）:
当执行第一次查询时，MyBatis会首先检查二级缓存中是否有结果。如果二级缓存中没有结果，它会查询数据库，并将结果同时放入一级缓存和二级缓存。
接着，当执行insert操作时，由于这个操作没有提交，它不会影响数据库中的实际数据，但MyBatis会认为数据已经改变，并清空所有相关的一级缓存和二级缓存。这意味着，如果其他SqlSession尝试从二级缓存中获取相同ID的商品，它们将不会看到insert操作的结果，因为缓存已经被清空。
由于insert操作没有提交，一级缓存和二级缓存都会被清空。这意味再进行查询，MyBatis将不得不重新查询数据库，而不是从缓存中获取结果。
3、在不同的代码中书写增删改操作，都可能会对一级缓存和二级缓存产生干扰，所以出现的结果是不同的。
祝学习愉快！
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