oracle RAC 底层进程介绍

 1.GSD global services daemon 
oracle官方文档的描述 
The Global Services Daemon (GSD) runs on each node with one GSD process per node. The GSD coordinates with the cluster manager to receive requests from clients such as the DBCA, EM, and the SRVCTL utility to execute administrative job tasks such as instance startup or shutdown. The GSD is not an Oracle instance background process and is therefore not started with the Oracle instance. 
GSD与rac的管理工具dbca srvctl oem进行交互，用来完成实例的启动关闭等管理任务。 
为了保证这些管理工具运行正常必须在所有的节点上先start gsd,并且一个GSD进程支持在 
一个节点的多个rac.gsd进程位于$ORACLE_HOME/bin目录下，其log文件为$oracle_home 
/srvm/log/gsdaemon.log 
例如： 
假设使用oem工具来启动一个实例，oem把该任务传递给相应的智能引擎，该智能引擎生成 
一个包含SRVCTL命令的脚本文件，GSD进程读取该脚本文件并且执行该脚本，最后GSD把 
执行结果返回给智能引擎,近而智能引擎返回给OEM. 
又例如假设使用srvctl工具关闭所有的实例，GSD进程接受来自SRVCTL工具发出的请求，并 
在本地节点上执行该请求，然后把执行结果返回给SRVCTL会话。 
2.LMON: Global Enqueue Service Monitor 
oracle官方文档的描述 
Global Enqueue Service Monitor (LMON) 
The background LMON process monitors the entire cluster to manage global resources. LMON manages instance deaths and the associated recovery for any failed instance. In particular, LMON handles the part of recovery associated with global resources. LMON-provided services are also known as Cluster Group Services. 
LMON主要监测群集内的全局队列和全局资源，管理实例和处理异常并相应的群集队列进行恢复操作。 
3.LMD: Global Enqueue Service Daemon 
oracle官方文档的描述 
Global Enqueue Service Daemon (LMD) 
The resource agent process that manages requests for resources to control access to blocks. The LMD process also handles deadlock detection and remote resource requests. Remote resource requests are requests ori