mycat启动的时候启动了三个模块
1：NIOConnector（负责链接mysql数据库，连接池以数据库为准不以链接字符串为准），
1：NIOAcceptor，ManagerConnectionFactory（管理模块，默认端口9066）
2：NIOAcceptor,ServerConnectionFactory（mysql服务模块，默认端口8066）
这里介绍下管理模块的启动流程
顺序图
NIO和AIO
mycat分别实现了NIO和AIO，由于linux当前没有真正实现AIO这里主要介绍NIO的流程。
NIO的Reactor与AIO的Proactor两种模式的场景区别：
下面是Reactor的做法：1. 等待事件响应 (Reactor job)2. 分发 “Ready-to-Read” 事件给用户句柄 ( Reactor job)3. 读数据 (user handler job)4. 处理数据( user handler job)下面再来看看真正意义的异步模式Proactor是如何做的：1. 等待事件响应 (Proactor job)2. 读数据 (Proactor job)3. 分发 “Read-Completed” 事件给用户句柄 (Proactor job)4. 处理数据(user handler job)mycat的NIO实现
Selector（选择器）是Java NIO中能够检测一到多个NIO通道，并能够知晓通道是否为诸如读写事件做好准备的组件。这样，一个单独的线程可以管理多个channel，从而管理多个网络连接。
Selector可以监听四种不同类型的事件：- Connect- Accept- Read- Write这四种事件用SelectionKey的四个常量来表示：- SelectionKey.OP_CONNECT- SelectionKey.OP_ACCEPT- SelectionKey.OP_READ- SelectionKey.OP_WRITE前面已经说了，NIO采用的Reactor模式：例如汽车是乘客访问的主体（Reactor），乘客上车后，到售票员（acceptor）处登记，之后乘客便可以休息睡觉去了，当到达乘客所要到达的目的地后，售票员将其唤醒即可。
核心顺序
mycat管理端的启动流程
1：new ManagerConnectionFactory extends FrontendConnectionFactory
2：new NIOReactorPool，new NIOReactor，new RW中new ConcurrentLinkedQueue<AbstractConnection>()而AbstractConnection中new NIOSocketWR
3：new NIOAcceptor中向反应堆中注册了OP_ACCEPT，该类继承了Thread然后start启动
accept
channel = serverChannel.accept(); channel.configureBlocking(false); FrontendConnection c = factory.make(channel); c.setAccepted(true); c.setId(ID_GENERATOR.getId()); NIOProcessor processor = (NIOProcessor) MycatServer.getInstance() .nextProcessor(); c.setProcessor(processor); LOGGER.info("accept"); NIOReactor reactor = reactorPool.getNextReactor(); reactor.postRegister(c); factory.make(channel)：最终构造了ManagerQueryHandler（管理命令解析器）和FrontendAuthenticator（mycat权限解析器）
reactor.postRegister(c)：把当前链接添加到reactor的registerQueue中并唤醒reactor的selector
read
在NIOReactor的registerQueue为空的时候run循环空运转，当上一步把accept的链接放到队列的时候则
for (;;) { ++reactCount; try { selector.select(500L); register(selector); keys = selector.selectedKeys(); for (SelectionKey key : keys) { AbstractConnection con = null; try { Object att = key.attachment(); if (att != null) { con = (AbstractConnection) att; if (key.isValid() && key.isReadable()) { try { con.asynRead(); } catch (IOException e) { con.close("program err:" + e.toString()); continue; } catch (Exception e) { LOGGER.debug("caught err:", e); con.close("program err:" + e.toString()); continue; } } if (key.isValid() && key.isWritable()) { con.doNextWriteCheck(); } } else { key.cancel(); } } catch (CancelledKeyException e) { if (LOGGER.isDebugEnabled()) { LOGGER.debug(con + " socket key canceled"); } } catch (Exception e) { LOGGER.warn(con + " " + e); } } } catch (Exception e) { LOGGER.warn(name, e); } finally { if (keys != null) { keys.clear(); } } register(selector)；也即
((NIOSocketWR) c.getSocketWR()).register(selector); 注册OP_READ事件
c.register();即FrontendConnection的register发送握手数据包con.asynRead();即NIOSocketWR的asynRead即
public void asynRead() throws IOException { LOGGER.info("asynRead"); ByteBuffer theBuffer = con.readBuffer; if (theBuffer == null) { theBuffer = con.processor.getBufferPool().allocate(); con.readBuffer = theBuffer; } int got = channel.read(theBuffer); con.onReadData(got); } con.onReadData(got);即AbstractConnection的onReadData这里拆包得到完成的数据包后调用
handler.handle(data);也即FrontendAuthenticator的handle在这里check user；check password；check schema如果失败则将失败信息写入缓冲区，如果成功
则把AbstractConnection的默认hander从FrontendAuthenticator换成FrontendCommandHandler等待接下来的处理（比如show命令等，
以上的处理是发生在输入mysql -utest -ptest -h10.97.177.83 -P9066时）
认证完成后下一次的handler.handle(data)则使用FrontendCommandHandler的handle来处理也即
public void handle(byte[] data) { if(source.getLoadDataInfileHandler()!=null&&source.getLoadDataInfileHandler().isStartLoadData()) { MySQLMessage mm = new MySQLMessage(data); int packetLength = mm.readUB3(); if(packetLength+4==data.length) { source.loadDataInfileData(data); } return; } switch (data[4]) { case MySQLPacket.COM_INIT_DB: commands.doInitDB(); source.initDB(data); break; case MySQLPacket.COM_QUERY: commands.doQuery(); source.query(data); break; case MySQLPacket.COM_PING: commands.doPing(); source.ping(); break; case MySQLPacket.COM_QUIT: commands.doQuit(); source.close("quit cmd"); break; case MySQLPacket.COM_PROCESS_KILL: commands.doKill(); source.kill(data); break; case MySQLPacket.COM_STMT_PREPARE: commands.doStmtPrepare(); source.stmtPrepare(data); break; case MySQLPacket.COM_STMT_EXECUTE: commands.doStmtExecute(); source.stmtExecute(data); break; case MySQLPacket.COM_STMT_CLOSE: commands.doStmtClose(); source.stmtClose(data); break; case MySQLPacket.COM_HEARTBEAT: commands.doHeartbeat(); source.heartbeat(data); break; default: commands.doOther(); source.writeErrMessage(ErrorCode.ER_UNKNOWN_COM_ERROR, "Unknown command"); } } source.query(data);即queryHandler.query(sql);这里的queryHandler是ManagerQueryHandler即
public void query(String sql) { ManagerConnection c = this.source; if (LOGGER.isDebugEnabled()) { LOGGER.debug(new StringBuilder().append(c).append(sql).toString()); } int rs = ManagerParse.parse(sql); switch (rs & 0xff) { case ManagerParse.SELECT: SelectHandler.handle(sql, c, rs >>> SHIFT); break; case ManagerParse.SET: c.write(c.writeToBuffer(OkPacket.OK, c.allocate())); break; case ManagerParse.SHOW: ShowHandler.handle(sql, c, rs >>> SHIFT); break; case ManagerParse.SWITCH: SwitchHandler.handler(sql, c, rs >>> SHIFT); break; case ManagerParse.KILL_CONN: KillConnection.response(sql, rs >>> SHIFT, c); break; case ManagerParse.OFFLINE: Offline.execute(sql, c); break; case ManagerParse.ONLINE: Online.execute(sql, c); break; case ManagerParse.STOP: StopHandler.handle(sql, c, rs >>> SHIFT); break; case ManagerParse.RELOAD: ReloadHandler.handle(sql, c, rs >>> SHIFT); break; case ManagerParse.ROLLBACK: RollbackHandler.handle(sql, c, rs >>> SHIFT); break; case ManagerParse.CLEAR: ClearHandler.handle(sql, c, rs >>> SHIFT); break; case ManagerParse.CONFIGFILE: ConfFileHandler.handle(sql, c); break; case ManagerParse.LOGFILE: ShowServerLog.handle(sql, c); break; default: c.writeErrMessage(ErrorCode.ER_YES, "Unsupported statement"); } } 总结
mycat的网络处理逻辑上是通过队列加上后台线程来实现了accept和read的解耦从而实现了高性能，但是代码写的就不敢恭维。