Oracle
Database is a relational database management system (RDBMS) that Oracle
Corporation created and marketed. It is one of the most popular RDBMSs on the
market and is used to store and retrieve data for a wide range of applications.
Oracle Database is well-known for its dependability, scalability, and
performance, and it is compatible with a wide range of programming languages
and development frameworks. It includes data warehousing, online transaction
processing, and advanced analytics, as well as high availability, disaster
recovery, and security.
Oracle
Database employs a client-server architecture, with the database server and
client connections running in separate processes. The server process manages
data and resources, and client connections communicate with the server to
access and manipulate data. SQL, PL/SQL (Oracle’s proprietary procedural
language), and Java are among the programming interfaces supported by Oracle
Database. It also includes tools for database management and administration,
such as Oracle Enterprise Manager and SQL Plus.
The
oracle database architecture consists of:
- Memory structure(Instances)
- Database system
- Processes
Oracle
Instances
The instance
is a collection of two things:
SGA: It stands for System Global Area. It
is a shared memory area. Whenever a database instance starts, some memory
gets allocated and that memory is termed SGA. Along with memory allocation, one
or more background processes will. SGA is used to store data as well as control
information about one database instance through its various subcomponents,
Where each component is dedicated to a specific purpose. Various Components
are:
- Database buffer cache: The Buffer Cache is a
portion of the SGA that stores copies of data blocks read from datafiles.
It is used to cache frequently accessed data blocks, reducing the number
of disks I/Os required to access the data. This can improve performance by
reducing disk I/O time and increasing the speed of data retrieval.
- Redo log Buffer: The most crucial structure for
recovery operations is the redo log, which consists of two or more
preallocated files that store all changes made to the database as they
occur. Every instance of an Oracle Database has an associated redo log to
protect the database in case of an instance failure.
- Java pool: The Java Pool is an
optional portion of the SGA that is used by Java Virtual Machine (JVM) and
related components. It is used to store Java-related data structures, such
as Java classes and objects. This pool is used when the Oracle Database is
configured to run Java applications or when using Oracle JVM.
- Large Pool: The Large Pool is an
optional portion of the SGA that can be used for large memory allocation,
such as backup and restore operations and I/O server processes. It is
typically used to improve the performance of these operations by reducing
the amount of disk I/O required.
- Shared pool: The Shared Pool is a portion of
the SGA that contains shared memory structures, such as shared SQL and
PL/SQL areas. It is used to store the parsed representation of SQL
statements, execution plans, and PL/SQL program units. This allows for the
efficient reuse of frequently executed statements, reducing the need for
reparsing and improving performance.
Background
processes: Oracle
has a collection of processes that are called background processes. These
processes are responsible for managing memory, performing I/O operations, and
other maintenance activities. Following are some important background
processes that are required:
- System Monitor Process (SMON): These processes are
responsible for performing system-level recovery and maintenance
activities.
- Process Monitor Process (PMON): The task of these
processes is to monitor other background processes.
- Database Writer Process
(DBWR): This
process performs the task of writing data blocks from the Database Buffer
Cache (present in SGA) to physical data files(Present in the Database
system).
- Log Writer Process (LGWR): This
process writes the Redo blocks from Redo Log Buffer (present in SGA) to
Redo Log Files(present in the Database system).
- CheckPoint (CKPT): This process maintains
data files and control files with the most recent checkpoint information.
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Database
System
The database
system is suited to the storage system of a computer. The Database system is
simply the storage of files. There are three categories of files that are
situated in the database system and those are:-
- Data files: These files hold the
actual data in the database.
- Redo log files: These files are used to
hold the changes made in the database. Redo log files can be utilized
during the database recovery process to retrieve the original information.
- Control files: It
is a binary file that holds database status-related information like
Database Name, Data File, and Redo Log file Names, File Locations, and Log
Sequence Number.
There are
other categories of files that contribute to database management.
- Parameter file: This file contains the
parameters which define the way the database is expected to start up.
- Password file: This file holds the user
passwords and thus maintains the security of databases.
Processes
There are
two types of processes:
- User process: It is also known as the client
process The user actually connects to the instance with the help of user
processes.
the user process is stabilized when the user sends a connection request to the oracle server. - Server process: The server Process
connects the user to the database and performs the activities on the
client’s behalf as executing SQL statements or retrieving data from the
database.
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