Oracle RAC instances and threads

1. Oracle cluster architecture
1. Oracle RAC is the Real Application Cluster of Oracle. It is a parallel Cluster system provided by Oracle. The entire Cluster system is composed of Oracle Cluster (Cluster ready software) and Real Application Clusters (RAC.
2. The essence of Oracle RAC is that Oracle instance nodes in different operating systems access the same Oracle database at the same time, and each node communicates through the private network to monitor the running status of each node; all data files, online log files, and control files of the Oracle database are stored in the cluster.
Shared storage devices can be RAW (without a file system), ASM, and OCFS2 (shared file system provided by oracle, all cluster nodes can read and write shared storage at the same time.
3. The basic topology of Oracle RAC is as follows:

4. the topology structure shows that:
An Oracle Rac database consists of multiple server nodes. Each server node has its own operating system, ClusterWare, and Oracle Rac database program, and each node has its own network listener. ClusterWare is a cluster software mainly used for cluster system management. The Oracle Rac database program is used to provide Oracle instance processes for clients to access the cluster system. The listening service is mainly used to listen on their network port information, all services and programs access a shared storage through the operating system, and finally complete data read and write. There are many ways to implement shared storage, including automatic storage management (ASM), Oracle Cluster File System (OCFS), Raw, and network region storage (NAS) to ensure the consistency of the entire cluster data.
5. Oracle provides its own Cluster software (Oracle Clusterware) starting from 10 Gb in Oracle, which is implemented through CRS (Cluster Ready Services). This software is a prerequisite for installing Oracle RAC, it is also the basis for stable operation of the RAC environment. In versions earlier than 10 Gb of Oracle, RAC must be installed using third-party cluster software in the domain. After 10 Gb of Oracle, when Oracle rac is installed, you can use the cluster software that comes with Oracle or a third-party cluster software that has been certified by RAC.
6. Common cluster Topology

 
7. From the Oracle operating mechanism, each server in the cluster is an Oracle instance. Multiple Oracle instances correspond to the same Oracle database and constitute an Oracle database cluster, database instances running on two nodes access the same RAC database, and the local disks of the two nodes are only used to store the Oralce installer and ClusterWare software, while on shared storage, it stores Oracle database files, control files, online log files, and archive log files. This is a data storage and distribution method when Oracle Rac is installed, in fact, RAC provides a variety of data storage methods.
2. Introduction to Oracle ClusterWare
1. Cluster Ready Services (CRS) is a Cluster software developed by Oracle. Similar to other Cluster software, CRS mainly implements Cluster member management, heartbeat monitoring, failover, and other functions, CRS requires that the operating systems of each cluster node must be the same. In this way, the operating systems of multiple nodes are bound through CRS, and the client accesses the cluster just like accessing a server.
2. CRS consists of two Cluster suites: Voting disk and Oracle Cluster Registry. Voting disk is the voting disk. each node in the cluster regularly evaluates its health status and puts its status information on the voting disk. In addition, the nodes view the running status of each other and pass the information to other nodes to write them to the voting disk. When a cluster node fails, the voting disk can also be used for voting and arbitration. Therefore, the voting disk must be placed on the shared storage device. To ensure that each node can be accessed. A voting disk can be a raw device partition or an independent file. Because it only records node running information, the disk size is generally about 10-20 mb.
3. Oracle Cluster Registry (OCR for short) is the Cluster registration service. OCR is used to record the configuration information of the Cluster and database in RAC. This information includes the list of cluster nodes, the ing between cluster database instances and nodes, and the CRS Application resource information. CRS uses two heartbeat Devices
To verify the status of node members and ensure the integrity of the cluster: a voting disk, the cluster synchronization service process writes a heartbeat message to the voting disk every several seconds, the cluster verifies the node status by voting on the disk. If a disk does not write information to the voting disk within the specified maximum time, the cluster determines that the node is invalid and implements failover. The heartbeat mechanism of the private Ethernet network between the other heartbeat nodes can be used to determine whether a network fault has occurred between the nodes. The combination of the two heartbeat mechanisms effectively increases the cluster reliability. In addition, CRS suggests that the private Ethernet Used for internal communication must be separated from the network used for communication between RAC nodes, that is, it cannot be in the same network, if the communication network between RAC nodes and the private Ethernet heartbeat are in the same network, you must ensure that the network cannot be accessed by nodes of non-cluster systems.
Iii. background processes of CRS
Oracle ClusterWare uses Cluster Ready Services to complete Cluster functions. CRS contains a group of background processes that work together. The following describes several important background processes in CRS.
1. Cluster Synchronization Services (CSS for short) is used to manage and coordinate the relationship between nodes in an emergency group and communicate between nodes. When a node joins or leaves a Cluster, all notifications are sent to the cluster by CSS. The CSS background process corresponding to the masses is CSSD, which is used by Oracle
User operation and management. When a node fails, cssd automatically restarts the operating system.
2. Cluster Ready Services (CRS) is the main program for managing high-availability operations in the Cluster. CRS manages all resources in the Cluster, including databases, services, instances, vip addresses, listeners, and application processes. The background process of CRS in the cluster is CRSD, this process can start, stop, monitor, and fault tolerance cluster resources. Under normal conditions, CRSD monitors various node resources. When a resource is abnormal, automatically Restart or switch the resource.
3. Process Monitor Daemon (OPROCD for short). The Process is locked in the memory. The user monitors the cluster and provides I/O protection (I/O fencing ). OPROCD runs on each node and regularly performs health checks. If the interval is exceeded, it still cannot communicate with a node process, then OPROCD will reset the processor and restart the node. An OPROCD failure also causes ClusterWare to restart the node.
4. Oracle Noification Service (ONS) is an Oracle Notification Service. It is mainly used to publish and subscribe to Fast Application Notification events.
5. Event Management (EVM) is an Event detection background process that is run and managed by Oracle users.
4. RAC database architecture Process
1. RAC database Introduction
RAC database is a cluster database with a shared Cache architecture. It overcomes the limitations of traditional methods of not sharing or sharing disks, A Scalable and available database solution is provided for all business applications. It generally forms an Oracle cluster system together with Oracle, clusterWare, or third-party cluster software.
2. the RAC database is a fully shared architecture. All its data files, control files, training log files, and parameter files must be stored on the shared disk, all nodes can be accessed. RAC supports multiple storage methods. You can use either of the following methods:
V. Storage of RAC Databases
1. Raw devices)
That is, data is directly stored and written to the disk without going through the file system. The advantage of this method is that the disk has high I/O performance and is suitable for business systems with frequent write operations, however, the disadvantages are also obvious: Data Maintenance and backup are inconvenient. Backup can only be performed through dd commands or block-level backup devices, which undoubtedly increases the maintenance cost.
2. Cluster File System
To support shared storage, Oralce developed the Cluster File System OCFS, which can be used for Windows, Linux, and Solaris. Now it has developed to OCFS2, through the OCFS2 file system, multiple cluster nodes can read and write a disk at the same time without damaging data. However, for a large number of read/write business systems, the performance is not very high. In addition, Oracle RAC also supports third-party cluster file systems, such as RedHat GFS.
3. Network File System (NFS)
4, Automatic Storage Management
Automatic Storage Management (ASM) is a recommended shared data Storage method in Oracle. It is a feature of Oracle Database 10 Gb. ASM actually stores data in RAW mode, but adds the data management function. It writes data directly to the disk to avoid I/O consumption through the file system. Therefore, using ASM can easily manage shared data and provide asynchronous I/O performance. ASM can also optimize performance by allocating I/O loads, eliminating the need to manually adjust I/O.

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