最近小组来了个新的小伙伴--小明！
然后在项目上了test环境后。在运行过程中，突然报了这样的错误。哦？一看就是数据库死锁的问题呀。新加的功能更新操作有点问题呀！
11:12:39.138 [http-nio-8070-exec-6] ERROR druid.sql.Statement - {conn-10005, pstmt-20171} execute error. update master_task_plan set is_instance=? where project_id=?
com.mysql.cj.jdbc.exceptions.MySQLTransactionRollbackException: Deadlock found when trying to get lock; try restarting transaction
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:123)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
at com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:953)
at com.mysql.cj.jdbc.ClientPreparedStatement.execute(ClientPreparedStatement.java:370)
at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:3409)
at com.alibaba.druid.filter.FilterAdapter.preparedStatement_execute(FilterAdapter.java:1081)
at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:3407)
at com.alibaba.druid.filter.FilterEventAdapter.preparedStatement_execute(FilterEventAdapter.java:440)
at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:3407)
at com.alibaba.druid.filter.FilterEventAdapter.preparedStatement_execute(FilterEventAdapter.java:440)
at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:3407)
at com.alibaba.druid.wall.WallFilter.preparedStatement_execute(WallFilter.java:627)
at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:3407)
at com.alibaba.druid.proxy.jdbc.PreparedStatementProxyImpl.execute(PreparedStatementProxyImpl.java:167)
at com.alibaba.druid.pool.DruidPooledPreparedStatement.execute(DruidPooledPreparedStatement.java:497)
at sun.reflect.GeneratedMethodAccessor216.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.ibatis.logging.jdbc.PreparedStatementLogger.invoke(PreparedStatementLogger.java:59)
at com.sun.proxy.$Proxy252.execute(Unknown Source)
at org.apache.ibatis.executor.statement.PreparedStatementHandler.update(PreparedStatementHandler.java:46)
at org.apache.ibatis.executor.statement.RoutingStatementHandler.update(RoutingStatementHandler.java:74)
at org.apache.ibatis.executor.SimpleExecutor.doUpdate(SimpleExecutor.java:50)
at org.apache.ibatis.executor.BaseExecutor.update(BaseExecutor.java:117)
at org.apache.ibatis.executor.CachingExecutor.update(CachingExecutor.java:76)
at sun.reflect.GeneratedMethodAccessor224.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.ibatis.plugin.Invocation.proceed(Invocation.java:49)
at com.bzl.bps.db.interceptor.InsertIdInterceptor.intercept(InsertIdInterceptor.java:75)
at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61)
at com.sun.proxy.$Proxy250.update(Unknown Source)
at sun.reflect.GeneratedMethodAccessor224.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:63)
at com.sun.proxy.$Proxy250.update(Unknown Source)
at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:198)
at sun.reflect.GeneratedMethodAccessor295.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:433)
at com.sun.proxy.$Proxy125.update(Unknown Source)
at org.mybatis.spring.SqlSessionTemplate.update(SqlSessionTemplate.java:294)
at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:62)
at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:59)
at com.sun.proxy.$Proxy152.updateInstance(Unknown Source)
at com.bzl.bps.planschedule.service.impl.MasterTaskPlanServiceImpl.saveTaskPlan(MasterTaskPlanServiceImpl.java:1074)
at com.bzl.bps.planschedule.service.impl.MasterTaskPlanServiceImpl.saveAsTaskPlan(MasterTaskPlanServiceImpl.java:543)
at com.bzl.bps.planschedule.service.impl.MasterTaskPlanServiceImpl$$FastClassBySpringCGLIB$$571c290e.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:771)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749)
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:367)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:118)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749)
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:691)
at com.bzl.bps.planschedule.service.impl.MasterTaskPlanServiceImpl$$EnhancerBySpringCGLIB$$e446eb3b.saveAsTaskPlan(<generated>)
at com.bzl.bps.planschedule.rest.MasterTaskPlanRest.saveAsTaskPlan(MasterTaskPlanRest.java:70)
at com.bzl.bps.planschedule.rest.MasterTaskPlanRest$$FastClassBySpringCGLIB$$7ba93760.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:771)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749)
at org.springframework.aop.aspectj.AspectJAfterAdvice.invoke(AspectJAfterAdvice.java:47)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749)
at org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor.invoke(MethodBeforeAdviceInterceptor.java:56)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:95)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749)
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:691)
at com.bzl.bps.planschedule.rest.MasterTaskPlanRest$$EnhancerBySpringCGLIB$$77c39170.saveAsTaskPlan(<generated>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:878)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:792)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:652)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at com.bzl.bps.utils.filer.XssFilter.doFilter(XssFilter.java:30)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at com.alibaba.druid.support.http.WebStatFilter.doFilter(WebStatFilter.java:124)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1589)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
“小明，你写的update操作有点问题，需要改改”
“我测试没啥问题的呀。babababala!~”
“没问题为啥会报错？你这报错前端就是系统异常。”
....
十分钟后，我不知道怎么复现的耶。哥，不如你教教我。
os:“明显你比我年纪大呀！”
这类问题主要发生在高并发、还有就是多个事务对同一个表做更新操作的时候引起的。显然他不知道为啥。
原因：
- 我们数据库用的是MySQL。
- 我们用的是MySQL的innodb引擎。
- innodb在更新时用的时行级锁。
- 行级锁锁的不是记录，而是锁的索引。
- 对于没有索引的操作会用表级锁。
再来看你写的sql。
update master_task_plan set is_instance=#{isInstance} where project_id=#{projectId}
主键索引是id列，然后给project_id添加了辅助索引。
调用这句sql的时候，会：
- 先给project_id索引上锁，然后根据project_id查询出主键id，
- 再获取主键索引的锁，然后根据主键id去查对应的值。
如果步骤1和2之间，来了一个事务B，
update master_task_plan set text="123" where id = #{id} and project_id=#{projectId}
那么就会：
a. 先给主键索引上锁，然后等待project_id索引。问题在步骤1，已经锁住了project_id索引，所以才会造成死锁呀！
根据主键索引更新数据的地方实在太多了。索引很有可能就发生死锁的情况了呀！
解决方案：
//1.先获取需要更新的记录的主键，给加个写锁（排他锁）
select id from user_item where user_id=? and item_id=? FOR UPDATE
//2. 逐条更新
...
真高兴小明你加入我们的团队啊！>_<
补充:
一般来说如果已经报错了，说明事务已经回滚了。只要有一个线程回滚了，那么另一个线程就可以继续执行。但如果特殊情况下，死锁没有消除。那么就需要用命令来将线程杀掉了。
查询是否锁表
show OPEN TABLES where In_use > 0;
查询到相对应的进程 === 然后 kill id
查询进程
show processlist
杀掉死锁的线程
KILL mysql的线程id
查看数据库当前的进程，看一下有无正在执行的慢SQL记录线程。
show processlist;
查看当前的事务
当前运行的所有事务
SELECT * FROM information_schema.innodb_trx;
当前出现的锁
SELECT * FROM information_schema.INNODB_LOCKs;
如果出现1109 - Unknown table 'INNODB_LOCKS' in information_schema则要使用👇下面语句
mysql8.0后，查询当前出现的锁
SELECT * FROM performance_schema.data_lock_waits;
锁等待的对应关系
SELECT * FROM information_schema.INNODB_LOCK_waits;
其实平时的项目中，还是wait lock比较常见。所以避免的方法还是：
-
delete update 操作避免使用非索引字段为条件，尽量使用主键索引来更新删除
