Oracle Database Architecture | Oracle Memory Structures

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• published: 24 Nov 2015
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Oracle DBA Course Info : http://goo.gl/jL4MF7 Oracle DBA: Oracle Database Administrator: A database administrator directs or performs all activities related to maintaining a successful database environment. The Responsibilities of DBA is designing, implementing, and maintaining the database. Versions: Oracle 10g, Oracle 11g……. ,g stands for grid Grid: Grid is basically a group of similar components that are working towards common task or common goal. In IT software grid means group of systems that are grouped together to perform a particular task. In earlier days there is having single server and it is not able to handle everything because when the workload increase and it was not sufficient to use. So there is a problem of reliability and scalability. Reliability means the system will give correct output in a given time. Scalability means, the system that can handle increasing numbers of requests without adversely affecting response time and throughput. To overcome these two issues First thing to achieve reliability, backup machine is used for instead of one machine. When one machine is gone down another one immediately carried out from that point onwards. To achieve scalability, instead of one machine they grouped all the softwares that were running on the machine, application related softwares, database related softwares and all the stored data was grouped and installed each of them in a single machine. Grid Architecture: Grid can be built with open source technology and oracle supports grid. They are having mainly three grids, so it is called as three tier architecture. Three tier architecture: Application grid: Combinations of all application servers considered as Application grid, oracle stream is software which is used to create application grid. Database grid: Combination of all database servers considered as Database grid, real application clusters is used to create Database grid. Storage grid: Combination of all database servers considered as storage servers, automatic storage management is used to create storage grid. To control above all of them have single tool that is “enterprise manager grid control”, it is used to manage all the different servers. Oracle features- •Low cost •High quality of service •Easy to manage Database Architecture: Database: A database is a collection of information that is organized so that it can easily be accessed, managed, and updated. It mainly consists of two components. Oracle instance: It is a collection of oracle memory processors and must allocate some memory to be used in database, which memory makes it as instance. it is a combination of system global area that is used for memory allocation and the background processors. Every instance has a unique name that oracle instance can exist without a database. Oracle database: Oracle database is a relational database management system from the Oracle Corporation. The system is built around a relational database framework in which data objects may be directly accessed by users through structure query language. Although the data is usually stored on a disk storage system, the database software manages how that data is stored and managed and the database can exist without an instance. All the physical files are stored in the database, when database is open then instance is available and when database is closed there is no longer instance is available. An oracle database uses memory structure and process to manage and access the data. All memory structures exist in the main memory of the computers that constitute the database server. Oracle memory structure: it is a combination of SGA and PGA Program Global Area: Private to each server and background process. There is one PGA for each process. A system global area is a group of shared memory structures that contain data and control information for one Oracle database instance. If multiple users are concurrently connected to the same instance, then the data in the instance's SGA is shared among the users. Consequently, the SGA is sometimes called the shared global area. The SGA contains the following data structures: Shared pool: caches various constructs that can be shared among users Java pool: it is used for all session specific java code and data within the java virtual machine. Streams pool: It is used by oracle streams. When you start the instance by using Enterprise Manager or SQL *plus, the amount of memory allocated for the SGA is displayed. Database buffer cache: caches blocks of data retrieved from the database Large pool: it is an optional area that provides large memory allocation for certain large processes, such as oracle backup and recovery operations, and I/O server processes. Redo log buffer: caches redo information based used for instance recovery until it can be written to the physical redo files stored on the disk.