Mysql併發保證數據一致性——實例

1. 背景

最近的項目中遇到一項問題，併發更新某一單據的時候，出現了更新失效的情況。比如：

@Transactional(rollbackFor = Exception.class)
public void update(Integer id){
    //1.按id查詢
    //2.更新某一字段的值
}

生成的SQL大概是這樣的：

UPDATE  table 
SET field = #{field,jdbcType=INTEGER}
WHERE id= 1

那麼以上代碼產生的問題就是：
對於同一個id=1來說，請求A與請求B都進到了update方法中，此時按id查詢得到的信息是相同的，那麼請求A更新了id=1的這條記錄之後，此時，請求B又對id=1的記錄進行更新，此時注意請求B更新id=1的記錄的時候，請求B按id查詢到的數據已經是舊數據了，請求B執行完之後，請求A的更新被請求B覆蓋了。

如果更新的是狀態，那倒無所謂，如果庫存量呢？
如果更新的是庫存，是在這條記錄的原始值上進行+或者-操作，是不是就出問題了？

2. 分析產生的原因

事後寫了個小demo來複現問題，代碼大致如下：

需求：某個分類每被訪問一次，排序就+1；
開啓兩個客戶端同時訪問

@Transactional(rollbackFor = Exception.class)
public void updateStatusTest(Integer id) {
    System.out.println("start:"+Thread.currentThread().getName());
    Category category = categoryMapper.selectById(id);
    try {
        Thread.sleep(8000);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    System.out.println(Thread.currentThread().getName()+":"+category);
    category.setSort(category.getSort()+1);
    categoryMapper.updateById(category);

    category = categoryMapper.selectById(id);
    System.out.println(Thread.currentThread().getName()+":"+category);
    System.out.println("end:"+Thread.currentThread().getName());
}

DAO層使用的mybatis，生成日誌大致如下：
需要更新的sort值數據庫初始爲：0

start:http-nio-8062-exec-1
Creating a new SqlSession
Registering transaction synchronization for SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6df7e3e9]
JDBC Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@2d5c951c] will be managed by Spring
==>  Preparing: SELECT cid,category_name,parent_id,image_url,icon_url,sort,status FROM t_admin_category WHERE cid=? 
==> Parameters: 6(Integer)
<==    Columns: cid, category_name, parent_id, image_url, icon_url, sort, status
<==        Row: 6, 1, 0, 11111, 1, 0, 1111
<==      Total: 1
Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6df7e3e9]
 Time：27 ms - ID：com.sxl.simple.shop.admin.category.mapper.CategoryMapper.selectById
Execute SQL：
    SELECT
        cid,
        category_name,
        parent_id,
        image_url,
        icon_url,
        sort,
        status 
    FROM
        t_admin_category 
    WHERE
        cid=6

start:http-nio-8062-exec-2
Creating a new SqlSession
Registering transaction synchronization for SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7af43046]
JDBC Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@700c5b36] will be managed by Spring
==>  Preparing: SELECT cid,category_name,parent_id,image_url,icon_url,sort,status FROM t_admin_category WHERE cid=? 
 Time：2 ms - ID：com.sxl.simple.shop.admin.category.mapper.CategoryMapper.selectById
Execute SQL：
    SELECT
        cid,
        category_name,
        parent_id,
        image_url,
        icon_url,
        sort,
        status 
    FROM
        t_admin_category 
    WHERE
        cid=6

==> Parameters: 6(Integer)
<==    Columns: cid, category_name, parent_id, image_url, icon_url, sort, status
<==        Row: 6, 1, 0, 11111, 1, 0, 1111
<==      Total: 1
Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7af43046]
http-nio-8062-exec-1:Category{cid=6, categoryName='1', parentId=0, imageUrl='11111', iconUrl='1', sort=0, status='1111'}
Fetched SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6df7e3e9] from current transaction
==>  Preparing: UPDATE t_admin_category SET category_name=?, parent_id=?, image_url=?, icon_url=?, sort=?, status=? WHERE cid=? 
==> Parameters: 1(String), 0(Integer), 11111(String), 1(String), 1(Integer), 1111(String), 6(Integer)
 Time：16 ms - ID：com.sxl.simple.shop.admin.category.mapper.CategoryMapper.updateById
Execute SQL：
    UPDATE
        t_admin_category 
    SET
        category_name='1',
        parent_id=0,
        image_url='11111',
        icon_url='1',
        sort=1,
        status='1111' 
    WHERE
<==    Updates: 1
        cid=6

Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6df7e3e9]
 Time：0 ms - ID：com.sxl.simple.shop.admin.category.mapper.CategoryMapper.selectById
Execute SQL：
Fetched SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6df7e3e9] from current transaction
    SELECT
        cid,
        category_name,
==>  Preparing: SELECT cid,category_name,parent_id,image_url,icon_url,sort,status FROM t_admin_category WHERE cid=? 
        parent_id,
==> Parameters: 6(Integer)
        image_url,
        icon_url,
<==    Columns: cid, category_name, parent_id, image_url, icon_url, sort, status
        sort,
        status 
<==        Row: 6, 1, 0, 11111, 1, 1, 1111
    FROM
<==      Total: 1
        t_admin_category 
    WHERE
Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6df7e3e9]
        cid=6

http-nio-8062-exec-1:Category{cid=6, categoryName='1', parentId=0, imageUrl='11111', iconUrl='1', sort=1, status='1111'}
end:http-nio-8062-exec-1
Transaction synchronization committing SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6df7e3e9]
Transaction synchronization deregistering SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6df7e3e9]
Transaction synchronization closing SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6df7e3e9]
http-nio-8062-exec-2:Category{cid=6, categoryName='1', parentId=0, imageUrl='11111', iconUrl='1', sort=0, status='1111'}
Fetched SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7af43046] from current transaction
==>  Preparing: UPDATE t_admin_category SET category_name=?, parent_id=?, image_url=?, icon_url=?, sort=?, status=? WHERE cid=? 
 Time：0 ms - ID：com.sxl.simple.shop.admin.category.mapper.CategoryMapper.updateById
Execute SQL：
    UPDATE
        t_admin_category 
    SET
        category_name='1',
        parent_id=0,
        image_url='11111',
        icon_url='1',
        sort=1,
        status='1111' 
    WHERE
        cid=6

==> Parameters: 1(String), 0(Integer), 11111(String), 1(String), 1(Integer), 1111(String), 6(Integer)
<==    Updates: 1
Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7af43046]
Fetched SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7af43046] from current transaction
==>  Preparing: SELECT cid,category_name,parent_id,image_url,icon_url,sort,status FROM t_admin_category WHERE cid=? 
==> Parameters: 6(Integer)
<==    Columns: cid, category_name, parent_id, image_url, icon_url, sort, status
<==        Row: 6, 1, 0, 11111, 1, 0, 1111
 Time：16 ms - ID：com.sxl.simple.shop.admin.category.mapper.CategoryMapper.selectById
Execute SQL：
    SELECT
        cid,
        category_name,
<==      Total: 1
        parent_id,
        image_url,
Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7af43046]
        icon_url,
        sort,
        status 
    FROM
http-nio-8062-exec-2:Category{cid=6, categoryName='1', parentId=0, imageUrl='11111', iconUrl='1', sort=0, status='1111'}
        t_admin_category 
end:http-nio-8062-exec-2
    WHERE
        cid=6

大致意思：
請求A與請求B，同時操作id=6的這條記錄時，查詢出來id=6的這條記錄，然後請求A對其進行了修改 SET　sort=1操作，完事之後，請求A的事務提交了。而此時請求B，通過id=6條件查詢到的category的信息是請求A提交之前的，此時請求B執行了SET　sort=1，覆蓋了請求B的修改操作。

3. 解決思路

解決方法其它很簡單，我們上面可以看到，update語句是直接set sort=1的，我們只需要改爲set sort = sort +1 就可以了。你不信？那我改一下試試：

@Transactional(rollbackFor = Exception.class)
public void updateStatusTest(Integer id) {
    System.out.println("start:"+Thread.currentThread().getName());
    Category category = categoryMapper.selectById(id);
    try {
        Thread.sleep(8000);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    System.out.println(Thread.currentThread().getName()+":"+category);
//        category.setSort(category.getSort()+1);
    categoryMapper.updateStatusById(category);

    category = categoryMapper.selectById(id);
    System.out.println(Thread.currentThread().getName()+":"+category);
    System.out.println("end:"+Thread.currentThread().getName());
}

Mapper文件：

<update id="updateStatusById" parameterType="com.sxl.simple.shop.admin.category.entity.Category">
      UPDATE
        t_admin_category
      SET
        sort =sort + 1
    WHERE
        cid= #{cid,jdbcType=INTEGER}
</update>

我們執行試一下，看下日誌：

start:http-nio-8062-exec-1
Creating a new SqlSession
Registering transaction synchronization for SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5e925f3f]
JDBC Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@6c17839b] will be managed by Spring
==>  Preparing: SELECT cid,category_name,parent_id,image_url,icon_url,sort,status FROM t_admin_category WHERE cid=? 
==> Parameters: 6(Integer)
<==    Columns: cid, category_name, parent_id, image_url, icon_url, sort, status
<==        Row: 6, 1, 0, 11111, 1, 0, 1111
<==      Total: 1
Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5e925f3f]
 Time：43 ms - ID：com.sxl.simple.shop.admin.category.mapper.CategoryMapper.selectById
Execute SQL：
    SELECT
        cid,
        category_name,
        parent_id,
        image_url,
        icon_url,
        sort,
        status 
    FROM
        t_admin_category 
    WHERE
        cid=6

start:http-nio-8062-exec-2
Creating a new SqlSession
Registering transaction synchronization for SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6c88f022]
JDBC Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@195f8b5a] will be managed by Spring
==>  Preparing: SELECT cid,category_name,parent_id,image_url,icon_url,sort,status FROM t_admin_category WHERE cid=? 
==> Parameters: 6(Integer)
<==    Columns: cid, category_name, parent_id, image_url, icon_url, sort, status
<==        Row: 6, 1, 0, 11111, 1, 0, 1111
<==      Total: 1
Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6c88f022]
 Time：2 ms - ID：com.sxl.simple.shop.admin.category.mapper.CategoryMapper.selectById
Execute SQL：
    SELECT
        cid,
        category_name,
        parent_id,
        image_url,
        icon_url,
        sort,
        status 
    FROM
        t_admin_category 
    WHERE
        cid=6

http-nio-8062-exec-1:Category{cid=6, categoryName='1', parentId=0, imageUrl='11111', iconUrl='1', sort=0, status='1111'}
Fetched SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5e925f3f] from current transaction
==>  Preparing: UPDATE t_admin_category SET sort =sort + 1 WHERE cid= ? 
==> Parameters: 6(Integer)
<==    Updates: 1
Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5e925f3f]
Fetched SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5e925f3f] from current transaction
==>  Preparing: SELECT cid,category_name,parent_id,image_url,icon_url,sort,status FROM t_admin_category WHERE cid=? 
 Time：0 ms - ID：com.sxl.simple.shop.admin.category.mapper.CategoryMapper.updateStatusById
Execute SQL：
    UPDATE
        t_admin_category 
    SET
        sort =sort + 1 
    WHERE
        cid= 6

==> Parameters: 6(Integer)
 Time：0 ms - ID：com.sxl.simple.shop.admin.category.mapper.CategoryMapper.selectById
<==    Columns: cid, category_name, parent_id, image_url, icon_url, sort, status
Execute SQL：
<==        Row: 6, 1, 0, 11111, 1, 1, 1111
    SELECT
<==      Total: 1
        cid,
Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5e925f3f]
        category_name,
        parent_id,
http-nio-8062-exec-1:Category{cid=6, categoryName='1', parentId=0, imageUrl='11111', iconUrl='1', sort=1, status='1111'}
        image_url,
end:http-nio-8062-exec-1
        icon_url,
        sort,
Transaction synchronization committing SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5e925f3f]
        status 
    FROM
Transaction synchronization deregistering SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5e925f3f]
        t_admin_category 
    WHERE
Transaction synchronization closing SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5e925f3f]
        cid=6

 Time：0 ms - ID：com.sxl.simple.shop.admin.category.mapper.CategoryMapper.updateStatusById
Execute SQL：
    UPDATE
        t_admin_category 
    SET
        sort =sort + 1 
    WHERE
        cid= 6

 Time：0 ms - ID：com.sxl.simple.shop.admin.category.mapper.CategoryMapper.selectById
Execute SQL：
    SELECT
        cid,
        category_name,
        parent_id,
        image_url,
        icon_url,
        sort,
        status 
    FROM
        t_admin_category 
    WHERE
        cid=6

http-nio-8062-exec-2:Category{cid=6, categoryName='1', parentId=0, imageUrl='11111', iconUrl='1', sort=0, status='1111'}
Fetched SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6c88f022] from current transaction
==>  Preparing: UPDATE t_admin_category SET sort =sort + 1 WHERE cid= ? 
==> Parameters: 6(Integer)
<==    Updates: 1
Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6c88f022]
Fetched SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6c88f022] from current transaction
==>  Preparing: SELECT cid,category_name,parent_id,image_url,icon_url,sort,status FROM t_admin_category WHERE cid=? 
==> Parameters: 6(Integer)
<==    Columns: cid, category_name, parent_id, image_url, icon_url, sort, status
<==        Row: 6, 1, 0, 11111, 1, 2, 1111
<==      Total: 1
Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6c88f022]
http-nio-8062-exec-2:Category{cid=6, categoryName='1', parentId=0, imageUrl='11111', iconUrl='1', sort=2, status='1111'}
end:http-nio-8062-exec-2

看到了吧，保證數據一致了吧

我之前的文章有對Mysql事務這塊做過詳解，想知道真正原理的小夥伴請閱讀：深入理解mysql事務
注意，我這裏使用的數據庫是mysql8以上，應用服務器是單機版的。

Mysql併發保證數據一致性——實例

1. 背景

2. 分析產生的原因

3. 解決思路

《Python進階》學習筆記

一個docker容器暴露多個端口

leetcode 60 排列序列

Leetcode 3161. 物塊放置查詢

微服務實踐之使用 Visual Studio 2022 調試Dapr 應用程序

wpf附加屬性理解 WPF附加屬性

MQ使用心得

淺談Linux Ext文件系統

分佈式系統中常用的負載均衡算法

redis實現分佈式鎖踩坑記錄

單點登錄系統SSO——理論

https://yachay.unat.edu.pe/blog/index.php?comment_area=format_blog&comment_component=blog&comment_co

linux以太網驅動總結