Cassandra源码解析系列启动模块

以3.11.4为基础

Cassandra 启动流程从bin下面的cassandra脚本开始进去看，会涉及到cassandra-env.sh进行进程启动的一些参数设置比如堆上内存分配，日志参数配置，基本环境设置等，我们直接看到启动的进程，也就是launch_service 这个函数,然后看到里面的exec 执行JAVA的进程，也就是class（launch_service参数传进来的classname为org.apache.cassandra.service.CassandraDaemon类）；大概的流程是：

cassandra -> lauch_service -> JAVA启动org.apache.cassandra.service.CassandraDaemon；

接下来就是看到org.apache.cassandra.service.CassandraDaemon这个类，直接在这个类里面通过main函数找到启动的入口：

 public static void main(String[] args) { instance.activate(); } 

在active函数里面有3个主要要看的函数：

 // Do not put any references to DatabaseDescriptor above the forceStaticInitialization call. try { applyConfig(); MBeanWrapper.instance.registerMBean(new StandardMBean(new NativeAccess(), NativeAccessMBean.class), MBEAN_NAME, MBeanWrapper.OnException.LOG); if (FBUtilities.isWindows) { // We need to adjust the system timer on windows from the default 15ms down to the minimum of 1ms as this // impacts timer intervals, thread scheduling, driver interrupts, etc. WindowsTimer.startTimerPeriod(DatabaseDescriptor.getWindowsTimerInterval()); } setup(); String pidFile = System.getProperty("cassandra-pidfile"); if (pidFile != null) { new File(pidFile).deleteOnExit(); } start(); } catch (Throwable e) { boolean logStackTrace = e instanceof ConfigurationException ? ((ConfigurationException)e).logStackTrace : true; System.out.println("Exception (" + e.getClass().getName() + ") encountered during startup: " + e.getMessage()); if (logStackTrace) { if (runManaged) logger.error("Exception encountered during startup", e); // try to warn user on stdout too, if we haven't already detached e.printStackTrace(); exitOrFail(3, "Exception encountered during startup", e); } else { if (runManaged) logger.error("Exception encountered during startup: {}", e.getMessage()); // try to warn user on stdout too, if we haven't already detached System.err.println(e.getMessage()); exitOrFail(3, "Exception encountered during startup: " + e.getMessage()); } } 

applyConfig();主要是用来初始化cassandra.yaml配置文件里的基本的配置，setup主要是做一些单节点初始化的时候的一些初始化工作，比如load本地的sstable元信息到内存，清除无用的sstable文件，启动的时候没有commit的transaction 执行或回滚，commitlog 的启动以及回放，集群元信息的效验，启动compaction，启动7000端口内部交流server等等事情；

start函数主要是启动9042的client监听端口，主要是netty的server，当然如果是thrift的话，也启动9160 端口服务；