Oracle Clusterware is designed for, and tightly integrated with, Oracle RAC.
When you create an Oracle RAC database using any of the management tools, the database is registered with and managed by Oracle Clusterware, along with the other Oracle processes such as Virtual Internet Protocol (VIP) address, Global Services Daemon (GSD), the Oracle Notification Service (ONS), and the Oracle Net listeners. These resources are automatically started when Oracle Clusterware starts the node and automatically restarted if they fail. The Oracle Clusterware daemons run on each node.
Oracle ClusterWare的进程组件：
Cluster Synchronization Services (CSS)--Manages the cluster configuration by controlling which nodes are members of the cluster and by notifying members when a node joins or leaves the cluster. If you are using third-party clusterware, then the css process interfaces with your clusterware to manage node membership information.
Cluster Ready Services (CRS)--The primary program for managing high availability operations within a cluster. Anything that the crs process manages is known as a cluster resource which could be a database, an instance, a service, a Listener, a virtual IP (VIP) address, an application process, and so on. The crs process manages cluster resources based on the resource's configuration information that is stored in the OCR. This includes start, stop, monitor and failover operations. The crs process generates events when a resource status changes. When you have installed Oracle RAC, crs monitors the Oracle instance, Listener, and so on, and automatically restarts these components when a failure occurs. By default, the crs process makes five attempts to restart a resource and then does not make further restart attempts if the resource does not restart.
Event Management (EVM)--A background process that publishes events that crs creates.
Oracle Notification Service (ONS)--A publish and subscribe service for communicating Fast Application Notification (FAN) events.
RACG--Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN events occur.
Process Monitor Daemon (OPROCD)--This process is locked in memory to monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the node. OPROCD uses the hangcheck timer on Linux platforms.
Unix系统Oracle Clusterware的后台进程:
crsd--Performs high availability recovery and management operations such as maintaining the OCR and managing application resources. This process runs as the root user, or by a user in the admin group on Mac OS X-based systems. This process restarts automatically upon failure.
evmd--Event manager daemon. This process also starts the racgevt process to manage FAN server callouts.
ocssd--Manages cluster node membership and runs as the oracle user; failure of this process results in cluster restart.
oprocd--Process monitor for the cluster. Note that this process only appears on platforms that do not use vendor clusterware with Oracle Clusterware.
Oracle RAC的Cache Fusion技术：
Oracle RAC databases have two or more database instances that each contain memory structures and background processes.
Each instance has a buffer cache in its System Global Area (SGA). Using Cache Fusion, Oracle RAC environments logically combine each instance's buffer cache to enable the instances to process data as if the data resided on a logically combined, single cache.
The SGA size requirements for Oracle RAC are greater than the SGA requirements for single-instance Oracle databases due to Cache Fusion.
GCS和GES服务与GRD的作用：
To ensure that each Oracle RAC database instance obtains the block that it needs to satisfy a query or transaction, Oracle RAC instances use two processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances, which effectively increases the size of the SGA for an Oracle RAC instance.
Cache Fusion的实现：
After one instance caches data, any other instance within the same cluster database can acquire a block image from another instance in the same database faster than by reading the block from disk. Therefore, Cache Fusion moves current blocks between instances rather than re-reading the blocks from disk. When a consistent block is needed or a changed block is required on another instance, Cache Fusion transfers the block image directly between the affected instances. Oracle RAC uses the private interconnect for interinstance communication and block transfers. The GES Monitor and the Instance Enqueue Process manages access to Cache Fusion resources and enqueue recovery processing.
RAC实现的几个后台进程：
The Oracle RAC processes and their identifiers are as follows:
LMS--Global Cache Service Process
LMD--Global Enqueue Service Daemon
LMON--Global Enqueue Service Monitor
LCK0--Instance Enqueue Process
