Oracle System Architecture

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Oracle was designed originally as a relational database management system (RDBMS). Starting with version 8 of the product, Oracle is being positioned as an object-relational database management system (ORDBMS). Our goal here is to review the features of Oracle including its relational and object-relational modeling facilities..An Oracle server consists of an Oracle database—the collection of stored data, including log and control files—and the Oracle Instance—the processes, including Oracle (system) processes and user processes taken together, created for a specific instance of the database operation. Oracle server supports SQL to define and manipulate data. In addition, it has a procedural language—called PL/SQL—to control the flow of SQL, to use variables, and to provide error-handling procedures. Oracle can also be accessed through general purpose programming languages such as C or JAVA.


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ORACLE SYSTEM : ORACLE SYSTEM Neenu Prasad

Oracle Database : Oracle Database A database is collection of data files plus programs that manipulate those data files Two types of information are stored in an Oracle database User data, relevant to a particular application System data, that the database needs to manage itself

PowerPoint Presentation : Architecture

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Oracle server : Oracle server An Oracle server consists of : Oracle database—the collection of stored data, including log and control files Oracle Instance—the processes, including Oracle (system) processes and user processes taken together, created for a specific instance of the database operation. Oracle server supports SQL to define and manipulate data, PL/SQL—to control the flow of SQL, to use variables, and to provide error-handling procedures. Oracle can also be accessed through general purpose programming languages such as C or JAVA.

Oracle database Components : Oracle database Components Database files – contain all database data Control files – contain info to access and manipulate the data Redo Logs – record all the transactions on the database Tablespaces – logical divisions of a database Segments – set of database blocks Extents – allocation of contiguous space on disk exp in bytes .

Oracle Database Structure : Oracle Database Structure Database files • An Oracle database consists of one or more database files. • These files contain data that can be accessed with the help of SQL. • A file can be associated with one and only one tablespace . • The database when created initially, has only one physical file. • The maximum number of files that can be opened at a time are 32 by default . • One or more physical files form a logical unit called tablespace .

Cont. : Cont. Control files • A database’s overall physical architecture is maintained by its control files. • These record control information about all the files within the database. • A control file is associated with a single database • Control files are automatically modified by Oracle; a user cannot edit them . • They are used to maintain internal consistency and guide recovery operations

Cont.. : Cont.. Redo Log files • A Redo Log contains all the transactions that have occurred against the database . • No activity in the database can take place without being recorded in Redo Logs . • The Redo Logs are necessary to protect against data loss. • Redo Logs are also called transaction logs. • Every database requires a minimum of two Redo Logs. • These are used in recovery operations to restore lost or damaged files.

TABLESPACES : TABLESPACES Tablespaces • A database is divided into logical divisions called tablespaces • A database may have one or more tablespaces • Each logical tablespace corresponds to one or more physical database files . •The typical tablespace present in an Oracle database are :

Cont.. : Cont.. SYSTEM – stores all information needed to manage itself TEMP – stores all temporary tables TOOLS – stores database objects needed to support different tools USER – information about users is stored DATA & INDEX – holds the actual data and the indexes ROLLBACK – where all undo information is stored

Segments & Extents : Segments & Extents Segments & Extents • All data in tablespace are stored in allocations of database space called segments . • For each table there is a table segment. For indexes so-called index segments are allocated. The segment associated with a database object belongs to exactly one tablespace . • An Oracle database requires upto five types of segments, viz : Data segments, Index segments, Rollback segments, Temporary segments , Bootstrap segments • An extent is an allocation of contiguous database space expressed in bytes

Oracle Instance : Oracle Instance the set of processes that constitute an instance of the server’s operation is called an Oracle Instance Consists of : System Global Area set of background processes.

System Global Area(SGA) : System Global Area(SGA) Shared memory area Oracle assigns an SGA area when an instance starts SGA is divided into 3 Database buffer cache: This keeps the most recently accessed data blocks from the database. Redo log buffer, which is the buffer for the redo log file and is used for recovery purposes. Shared pool, which contains shared memory constructs Eg : shared SQL areas,

User processes : User processes Each user process corresponds to the execution of some application (for example, an Oracle Forms application) or some tool

Program global area (PGA) : Program global area (PGA) This is a memory buffer that contains data and control information for a server process. A PGA is created by Oracle when a server process is started.

Oracle Processes : Oracle Processes Oracle creates server processes to handle requests from connected user processes The background processes are created for each instance of Oracle; they perform I/O asynchronously and provide parallelism for better performance and reliability.

background processes : background processes Database Writer (DBWR): Writes the modified blocks from the buffer cache to the data files on disk. Log writer (LGWR): Writes from the log buffer area to the on-line disk log file. Checkpoint (CKPT): Refers to an event at which all modified buffers in the SGA since the last checkpoint are written to the data files System monitor (SMON): Performs instance recovery, manages storage areas by making the space contiguous, and recovers transactions skipped during recovery.

Cont.. : Cont.. Process monitor (PMON): Performs process recovery when a user process fails. It is also responsible for managing the cache and other resources used by a user process . Archiver (ARCH): Archives on-line log files to archival storage (for example, tape) if configured to do so. Recoverer process (RECO): Resolves distributed transactions that are pending due to a network or systems failure in a distributed database

Cont.. : Cont.. Dispatchers ( Dnnn ): In multithreaded server configurations, route requests from connected user processes to available shared server processes. There is one dispatcher per standard communication protocol supported . Lock processes ( LCKn ): Used for inter-instance locking when Oracle runs in a parallel server mode.

Oracle Startup and Shutdown : Oracle Startup and Shutdown Starting a database Starting an instance of the database Mounting a database Opening a database

Oracle Startup and Shutdown : Oracle Startup and Shutdown Shutdown Close the database. Dismount the database. Shut down the Oracle instance.

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