Oracle Database Architecture Overview

Posted by Shaik Ahmed Ali on November 10, 2020 | 1 comment

 

Database: Database is the set or collection of data which can access through an Application and SQL stored in a structured manner in a server and resides on the physical disk.

Relational Database Management System(RDBMS):

      RDBMS is a type of DBMS where the data is stored in the form of Tables and the relation between the tables is also done based on Constraints. We can read the data using SQL.

Oracle database is one of the RDBMS (Relational Database Management System) which stores the data in the form of tables.     

  Oracle database consist of following components:

·         Instance

·         Background Process

·         Memory (SGA + PGA)

·         Database file

a)      Control files

b)      Datafiles

c)      Redo log files

Oracle Instance:

   Oracle instance is the combination of Background Process and Memory Structure (SGA+ PGA).

Oracle instance have some stages like nomount, mount, and open. You can only access the database when the instance is open. To start the instance, we need a file called parameter file. Single instance is associated to single database but you can have many instances running on the single server depends on specification (Memory) of the server.

Background Process:

 To establish a user connection oracle database system uses many background processes, BP perform the I/O operations and monitor other oracle processes to provide the parallelism to improve the performance of the database or query. Some of the BP are

1)      Server Process (SMON)

2)      Process Monitor (PMON)

3)      Log Writer (LGWR)

4)      Database Writer (DBW0)

5)      Checkpoint Process (CKPT)

6)      Archive Process (ARC0)

Memory (SGA + PGA):

Memory structure in oracle database consist of 2 components are:

1)      System Global Area (SGA)

2)      Program Global Area (PGA)

 

1)      System Global Area (SGA):

    The SGA is the shared global area which is shared by all the background processes and server to access the database. SGA also contains the information of cache data blocks, query execution plan, shared SQL Areas of the oracle database instance. SGA is allocated in the memory of the server.

    SGA also have its own components which are:

·         Database Buffer Cache

·         Redo Log Buffer

·         Shared Pool

2)      Program Global Area (PGA):

    The PGA is also a memory component which stores the data and information of server process. It is different from SGA where all the process shared the same memory but in the case of PGA it is allocated to the single process or thread. There will be one PGA for single process for example if you have 10 process then there will be 10 PGA allocated.

 

Database Files:

          Database contains several types of files which helps to run the database.

1)      Control files: control files contain the information of database like where the datafiles are located and Rman backup information use for recovery and restore purposes.

2)      Datafiles: datafiles contains the actual data and in the form of tables, indexes

3)      Redo Log files:  these files contain the information of change block or in simple words the transaction log happening on the database.

So in this blog you read about the overview architecture of oracle database in the next blog I will explain in depth of memory and process architecture and database files.