Oracle Database Architecture

Being an Oracle DBA or Oracle APPS DBA you should know the essence of the Database Architecture. Here I have attempted to clarify the essential of the Oracle Database Architecture in basic words. Not just for DBA this can help to all who are dealing with Oracle Products and on various Oracle Modules. 

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Explain the Oracle Architecture? 

Oracle Instance: 

A way to get to an Oracle database always opens one and just a single database and comprises of memory structures and foundation process. 

Oracle server: 

A DBMS that gives an open, far-reaching, coordinated way to deal with data management, Consists of an Instance and a database. 

Oracle database: 

Accumulation of information that is treated as a unit, Consists of Datafiles, Control records, Redo log documents. (discretionary param record, passwd document, chronicled log) 

Instance memory Structures: 

System Global Area (SGA): 

Assigned at case startup, and is a major segment of an Oracle Instance. 

SGA Memory structures: 

Incorporates Shared Pool, Database Buffer Cache, Redo Log Buffer among others. 

Shared Pool : 

Comprises of two key execution-related memory structures Library Cache and Data Dictionary Cache. 

Library Cache: 

Stores data about the most as of late utilized SQL and PL/SQL explanations and empowers the sharing of normally utilized articulations. 

Data Dictionary Cache : 

Stores accumulation of the most as of late utilized definitions in the database Includes db records, tables, lists, sections and so on. Improves perf. During the parse stage, the server procedure takes a gander at the information lexicon for data to determine item names and approve get to. 

Database Buffer Cache: 

Stores duplicates of information hinder that have been recovered from the datafiles. Everything is done here. 

Redo Log Buffer : 

Records all progressions made to the database information squares, Primary reason for existing is recuperation. Re-try sections contain data to remake or re-try changes. 

User process: 

Begun at the time a database User demands associated with the Oracle server. demands cooperation with the Oracle server, does not communicate legitimately with the Oracle server. 

Server process: 

Associates with the Oracle Instance and is Started when a client builds up a session. 

satisfies calls produced and returns results. 

Every server procedure has its very own nonshared PGA when the procedure starts. 

Server Process Parses and run SQL articulations issued through the application, Reads fundamental information obstructs from datafiles on circle into the common database cushions of the SGA, if the squares are not effectively exhibit in the SGA and Return brings about such a way, that the application can process the data. 

In certain circumstances when the application and Oracle Database work on a similar PC, it is conceivable to consolidate the client procedure and relating server process into a solitary procedure to diminish framework overhead. 

Program Global Area (PGA): 

Memory zone utilized by a solitary Oracle server process. 

Distributed when the server procedure is begun, deallocated when the procedure is ended and utilized by just one procedure. 

Used to process SQL articulations and to hold logon and other session data. 

Foundation forms: 

Begun when an Oracle Instance is started. 

Foundation Processes Maintains and implements connections among physical and memory structures 

There are two kinds of database forms: 

• Mandatory background process 

• Operational background forms 

Mandatory background process: 

– DBWn, PMON, CKPT, LGWR, SMON 

Operational background process: 

– ARCn, LMDn, RECO, CJQ0, LMON, Snnn, Dnnn, Pnnn, LCKn, QMNn 

DBWn writes when: 

Checkpoint happens 

Filthy cradles achieve edge 

There are no free cushions 

Break happens 

RAC ping solicitation is made 

Tablespace OFFLINE 

Tablespace READ ONLY 

Table DROP or TRUNCATE 

Tablespace BEGIN BACKUP 

Log Writer (LGWR) composes: 

At submit 

Whenever 1/third full 

At the point when there is 1 MB of re-try 

At regular intervals 

Before DBWn composes 

System Monitor (SMON) Responsibilities: 

-   Instance recovery

–  Rolls forward changes in re-try logs 

– Opens database for client get to 

– Rolls back uncertain exchanges 

   Blends free space 

    Deallocates impermanent fragments. 

Procedure Monitor (PMON) Cleans up after bombed forms by: 

Rolling back the transaction

Releasing locks 

Releasing other resources

Restarting dead dispatchers 

Checkpoint (CKPT) Responsible for: 

Flagging DBWn at checkpoints 

Refreshing datafile headers with checkpoint data 

Refreshing control documents with checkpoint data 

Archiver (ARCn) 

Discretionary foundation process 

Consequently chronicles online re-try logs when ARCHIVELOG mode is set 

Jam the record of all progressions made to the database 

What is the contrast between Oracle SID and Oracle administration name? 

Oracle SID is the remarkable name that particularly recognizes your occurrence/database whereas the administration name is the TNS pseudonym can be same or distinctive as SID. 

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