An Oracle RAC database has the same processes and memory structures as a single-instance Oracle database and additional process and memory structures that are specific to Oracle RAC. The global cache service and global enqueue service processes, and the global resource directory (GRD) collaborate to enable cache fusion. The Oracle RAC processes and their identifiers are as follows:
| ACMS | Atomic Control File to Memory Service |
|---|---|
| GTX[0-j] | Global Transaction Process |
| LMON | Global Enqueue Service Monitor |
| LMD | Global Enqueue Service Daemon |
| LMS | Global Cache Service Process |
| LCK0 | Instance Enqueue Process |
| LMHB | Global Cache/Enqueue Service Heartbeat Monitor |
| PING | Interconnect Latency Measurement Process |
| RCBG | Result Cache Background Process |
| RMSn | Oracle RAC Management Processes |
| RSMN | Remote Slave Monitor |
- Atomic Control File to Memory Service (ACMS): In a RAC environment, the ACMS per-instance process is an agent that contributes to ensuring a distributed SGA memory update is either globally committed if successful, or globally aborted if a failure occurs.
- Global Transaction Process (GTX[0-j]): The GTX[0-j] processes provide transparent support for XA global transactions in a RAC environment. The database automatically tunes the number of these processes based on the workload of XA global transactions.
- Global Enqueue Service Monitor (LMON): The LMON process monitors global enqueues and resources across the cluster and performs global enqueue recovery operations.
- Global Enqueue Service Daemon (LMD): The LMD process manages incoming remote resource requests within each instance.
- Global Cache Service Process (LMS): The LMS process maintains records of the data file statuses and each cached block by recording information in the 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.
- Instance Enqueue Process (LCK0): The LCK0 process manages noncache fusion resource requests such as library and row cache requests.
- Global Cache/Enqueue Service Heartbeat Monitor (LMHB): LMHB monitors LMON, LMD, and LMSn processes to ensure they are running normally without blocking or spinning.
- Interconnect Latency Measurement Process (PING): Every few seconds, the process in one instance sends messages to each instance. The message is received by PING on the target instance. The time for the round trip is measured and collected.
- Result Cache Background Process (RCBG): This process is used for handling invalidation and other messages generated by server processes attached to other instances in Oracle RAC.
- 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.
- Remote Slave Monitor (RSMN): The RSMN process 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.