Oracle RAC Components

In an application environment, all servers use and manage the same database to distribute the workload of each server. The hardware requires at least two servers, A shared storage device is also required. At the same time, two types of software are required: Cluster software and RAC components in the Oracle database. At the same time, the operating systems on all servers should be the same type of OS. According to the Configuration Policy of Server Load balancer, after a client sends a request to the listener of a service, based on our load balancing policy, this server may send requests to the RAC components of the Local Machine for processing or to the RAC components of another server for processing. After processing the requests, RAC accesses our shared storage devices through cluster software.

Logically, each node in the cluster has an independent linstance, which accesses the same database. Nodes communicate with each other through the communication layer of the cluster software. At the same time, a global cache service exists to reduce IO consumption. Therefore, the linstance of each database retains the same database cacheI.

RAC features:

Each node's linstance has its own SGA

Each node's linstance has its own background process.

Each node's linstance has its own redo logs.

Each node's linstance has its own undo tablespace.

All nodes share one copy of datafiles and controlfiles.

A Cache fusion technology is also proposed)

There are two purposes:

01. Ensure cache consistency

02. Reduce disk I/O consumption

Therefore, multiple nodes in the RAC environment retain the same database CACHE.

How Cache fusion works:

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01. One node reads a block from the shared database to the database cache.

02. This node performs cross db block copy on all nodes

03. When the cache of any node is modified, the cache is modified between nodes.

04. In order to achieve consistent storage, the final modification results will also be written to the disk.

ClusterWare component

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Four services

Crsd-Cluster Resource Service

Cssd-cluster Synchronization Service

Evmd-Event Management Service

Oprocd-node detection and monitoring

Three types of resources

VIP-Virtual IP Address)

OCR-Oracle Cluster Registry (Cluster registration file), which records information about each node

Voting Disk-Establishes quorum (Voting Disk). The arbitration mechanism is used to subscribe the behavior of multiple nodes simultaneously writing to the shared node, so as to avoid conflicts.

RAC Components

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Additional processes are provided to maintain the database.

LMS-Gobal Cache Service Process global Cache Service Process

LMD-Global Enqueue Service Daemon Global query Service Daemon

LMON-Global Enqueue Service Monitor Global query Service monitoring process

LCK0-Instance Enqueue Process Instance Query Process

Oracle RAC can also be built on large SMP hosts. IBM's AIX Series servers are usually high-end platforms, while Intel Linux is often used as its low-end platform. When aix unix is used to run Oracle RAC as a large-scale database system platform, its cluster system construction, implementation, O & M, and high availability settings have platform features.