本文摘抄录oracle官方文档，oracle rac使用的后台进程，用以备忘，记录之。

About Oracle RAC Background Processes

The GCS and GES processes, and the GRD collaborate to enable Cache Fusion. The Oracle RAC processes and their identifiers are as follows

ACMS: Atomic Controlfile to Memory Service (ACMS)

In an Oracle RAC environment, the ACMS per-instance process is an agent that contributes to ensuring a distributed SGA memory update is either globally committed on success or globally aborted if a failure occurs.

GTX0-j: Global Transaction Process

The GTX0-j process provides transparent support for XA global transactions in a RAC environment. The database autotunes the number of these processes based on the workload of XA global transactions.

LMON: Global Enqueue Service Monitor

The LMON process monitors global enqueues and resources across the cluster and performs global enqueue recovery operations.

LMD: Global Enqueue Service Daemon

The LMD process manages incoming remote resource requests within each instance.

LMS: Global Cache Service Process

The LMS process maintains records of the data file statuses and each cached block by recording information in a Global Resource Directory (GRD). The LMS process also controls the flow of messages to remote instances and manages global data block access and transmits block images between the buffer caches of different instances. This processing is part of the Cache Fusion feature.

LCK0: Instance Enqueue Process

The LCK0 process manages non-Cache Fusion resource requests such as library and row cache requests.

RMSn: Oracle RAC Management Processes (RMSn)

The RMSn processes perform manageability tasks for Oracle RAC. Tasks accomplished by an RMSn process include creation of resources related to Oracle RAC when new instances are added to the clusters.

RSMN: Remote Slave Monitor manages background slave process creation and communication on remote instances. These background slave processes perform tasks on behalf of a coordinating process running in another instance.

关于LMS进程说明

LMS: Global Cache Service Process

The LMS process maintains records of the data file statuses and each cached block by recording information in a Global Resource Directory (GRD). The LMS process also controls the flow of messages to remote instances and manages global data block access and transmits block images between the buffer caches of different instances. This processing is part of the Cache Fusion feature.

全局cache服务进程：

LMS进程用户维护rac数据文件的状态记录。及两点之前cached block(缓存数据块)

LMS进程控制远程instance之间的信息传播，以及不同instances之前的global data block的访问和 block images传输。

当一个instances需要访问远程instances的block images时，则需要通过lms进程传输，这个是cache fusion的功能特点。 这样就不用直接从本地disk加载文件到数据库的buffer cache当中了。

通过cache fusion特性实现数据块的快速访问，减少IO

LMS进程依赖instances节点之间的私有心跳地址传输，以保障传输速度，而此若private network interface card之前的通信出问题时，则此进程可能将数据库instance abort掉的。

所以，当LMS报错时，可以考虑pirvate ip所对应的网络连接是否出问题，来帮助诊断问题。