Oracle 4

WHY ORACLE ? Oracle is an open system i.e. the database is accessing by different data access languages like SQL, Visual Basic, Power Builders,Delphi,VC++,JAVA etc. Oracle supports database upto gigabytes in size. * Oracle supports large number of concurrent users. * Oracle supports true client/server environment.if enable processing to be spilt between database server and the client application programs. * Oracle provides high levelof data security in terms of users, passwords privileges, and permissions. * Oracle database behaves same on all platform line Windows,Unix,Dos,Mainframes etc.
Structure of Oracle Database:
physical structure: one or more data files, Two of more log files, One control file. Logical structure: Table spaces, Segments, Extents, Data blocks.
The data files contain all user data in terms of tables, index, and views. The log files contain the information to open and be recovered, of Undone after a transaction(Rollback).
The control file physical data, media information to open and manage data files .If the control file is damaged the server will not be able to open are use the database even if
the database is undamaged.
What are the Back ground processes in Oracle and what are they. ? There are basically 9 Processes but in a general system we need to mention the first five background processes. They do the house keeping activities for the Oracle and are common
in any system. a) Data Base Writer(DBWR) :: Data Base Writer Writes Modified blocks from Database buffer cache to Data Files.This is required since the data is not written whenever a transaction is commited. b)LogWriter(LGWR) :: LogWriter writes the redo log entries to disk. Redo Log data is generated in redo log
buffer of SGA. As transaction commits and log buffer fills, LGWR writes log entries into a online
redo log file. c) System Monitor(SMON) :: The System Monitor performs instance recovery at instance startup. This is useful for recovery from system failure. d)Process Monitor(PMON) :: The Process Monitor peforms process recovery when user Process fails. Pmon Clears and Frees resources that process was using. e) CheckPoint(CKPT) :: At Specified times, all modified database buffers in SGA are written to data files by DBWR at Checkpoints and Updating all data files and control files of database to indicate
the most recent checkpoint. f)Archieves(ARCH) :: The Archiver copies online redo log files to archival storal when they are busy. g) Recoveror(RECO) :: The Recoveror is used to resolve the distributed transaction in network h) Dispatcher (Dnnn) :: The Dispatcher is useful in Multi Threaded Architecture i) Lckn :: We can have upto 10 lock processes for inter instance locking in parallel sql.