Introduction and core concepts of Oracle RAC

Introduction and core concepts of Oracle RAC (Real Application Clusters)

With the continuous growth of enterprise data and the increasingly prominent demand for high availability and high performance, databases Clustering technology is becoming increasingly important. Oracle RAC (Real Application Clusters) is designed to solve this problem. Oracle RAC is a high-availability, high-performance cluster database solution launched by Oracle. It allows multiple database instances to run on different servers and share a storage space, thereby achieving horizontal expansion and load balancing of the database. Greatly improve the availability and performance of the database system.

The core concepts of Oracle RAC mainly include the following points:

1. Shared storage: Each instance of Oracle RAC can access shared storage, and shared storage usually It is provided by SAN (Storage Area Network) or NAS (Network Attached Storage), so that multiple instances can access database files at the same time, achieving data sharing and consistency.
2. Cluster architecture: Oracle RAC adopts a cluster architecture. Each node in the cluster runs a database instance. These instances communicate with each other through high-speed networks and can access shared storage at the same time, thus Achieved horizontal expansion and load balancing of the database.
3. Transparent failover: Oracle RAC has an automatic failover function. When a node in the cluster fails, the system will automatically switch the resources on the failed node to other normal nodes. Ensure high availability of the system.
4. Cache sharing: Different instances of Oracle RAC share data block cache through high-speed network, which can reduce I/O operations and improve system performance.
5. Data consistency: Oracle RAC ensures data consistency through Cache Fusion technology. When one instance modifies the data block, it will notify other instances to update the data block, thus ensuring Data consistency.

Below, we use a simple code example to illustrate the application scenarios and operation methods of Oracle RAC:

Assume we have an Oracle RAC cluster and there are two nodes Node1 in the cluster and Node2, each node runs an Oracle database instance. We need to create a table t_example, insert data on two nodes, and then verify the consistency of the data through queries.

First, create table t_example on Node1:

CREATE TABLE t_example ( id NUMBER PRIMARY KEY, name VARCHAR2(50) );

Then, insert data on Node1 and Node2 respectively:

Execute on Node1:

INSERT INTO t_example VALUES (1, 'Alice');

Execute on Node2:

INSERT INTO t_example VALUES (2, 'Bob');

Finally, query the data on any node and verify the consistency of the data:

SELECT * FROM t_example;

Through the above example, we can see that Oracle RAC allows multiple Nodes access shared data simultaneously and ensure data consistency, thereby achieving high availability and high performance.

In general, Oracle RAC is a powerful cluster database solution that can meet the needs of enterprises for high availability, performance and scalability. By properly configuring and managing Oracle RAC clusters, we can give full play to its advantages, improve the stability and performance of the database system, and meet the needs of enterprise development.

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