分库分表之ShardingSphere读写分离源码分析

逃离我推掉我的手 2023-06-25 02:21 29阅读 0赞

1. 问题

> 读写分离如何执行

2. 源码

ShardingMasterSlaveRouter为核心入口

>  
> 
>     public SQLRouteResult route(SQLRouteResult sqlRouteResult) {
>         Iterator var2 = this.masterSlaveRules.iterator();
>     
>         while(var2.hasNext()) {
>             MasterSlaveRule each = (MasterSlaveRule)var2.next();
>             // 开始路由
>             this.route(each, sqlRouteResult);
>         }
>     
>         return sqlRouteResult;
>     }

>     private void route(MasterSlaveRule masterSlaveRule, SQLRouteResult sqlRouteResult) {
>         Collection<RoutingUnit> toBeRemoved = new LinkedList();
>         Collection<RoutingUnit> toBeAdded = new LinkedList();
>         Iterator var5 = sqlRouteResult.getRoutingResult().getRoutingUnits().iterator();
>     
>         while(var5.hasNext()) {
>             RoutingUnit each = (RoutingUnit)var5.next();
>             if (masterSlaveRule.getName().equalsIgnoreCase(each.getDataSourceName())) {
>                 toBeRemoved.add(each);
>                 String actualDataSourceName;
>                 // 判断是否走主库
>                 if (this.isMasterRoute(sqlRouteResult.getSqlStatementContext().getSqlStatement())) {
>                     MasterVisitedManager.setMasterVisited();
>                     actualDataSourceName = masterSlaveRule.getMasterDataSourceName();
>                 } else {
>                 //  从库如果有多个，默认是轮询，也可以选择随机访问策略
>                     actualDataSourceName = masterSlaveRule.getLoadBalanceAlgorithm().getDataSource(masterSlaveRule.getName(), masterSlaveRule.getMasterDataSourceName(), new ArrayList(masterSlaveRule.getSlaveDataSourceNames()));
>                 }
>     
>                 toBeAdded.add(this.createNewRoutingUnit(actualDataSourceName, each));
>             }
>         }
>     
>         sqlRouteResult.getRoutingResult().getRoutingUnits().removeAll(toBeRemoved);
>         sqlRouteResult.getRoutingResult().getRoutingUnits().addAll(toBeAdded);
>     }

判断是否走主库，包括hint和非查询操作等

>     private boolean isMasterRoute(SQLStatement sqlStatement) {
>         return this.containsLockSegment(sqlStatement) || !(sqlStatement instanceof SelectStatement) || MasterVisitedManager.isMasterVisited() || HintManager.isMasterRouteOnly();
>     }
> 
> // HintManager可以设置强制走主库，或者非查询操作走主库
> 
>

RoundRobinMasterSlaveLoadBalanceAlgorithm类执行轮询查询从库策略

>     // 轮询访问从库
>     @Override
>     public String getDataSource(final String name, final String masterDataSourceName, final List<String> slaveDataSourceNames) {
>         AtomicInteger count = COUNTS.containsKey(name) ? COUNTS.get(name) : new AtomicInteger(0);
>         COUNTS.putIfAbsent(name, count);
>         count.compareAndSet(slaveDataSourceNames.size(), 0);
>         // 计数器来实现轮询
>         return slaveDataSourceNames.get(Math.abs(count.getAndIncrement()) % slaveDataSourceNames.size());
>     }