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| Oracle Database Server |
Oracle database server includes instance and daranase.
Insatance
Oracle Database Instance is nothing but combination of
- Background Process
- Memory Structure
Background process (DBW0,PMON, RECO,CKPT,SMON, LGWR and others). Background process is basically know as computer program.These process performs input/output operations.
------Memory Structure
When oracle database instance is started,memory structure (SGA)system global area is been created.Immediately the background processes also starts. The oracle Database instance gives access to an oracle database. An oracle Database Instance opens one and only one database.
Memory Structure includes two area of memory
1)(SGA)System Global Area---This is created when an instance is started.
2)(PGA)Program Global Area--This is created when a process at server starts up.
SGA
The system global area is in memory which is used to store the information shares by all database process and by all users of database.The information includes both organization data and control info used by the oracle server.The system global area is created in virtual memory.The size of SGA is established by the parameter SGA_MAX_SIXE ..
PGA
The Program Global Area is also termed as Process Global Area(PGA) and is a part of memory allocated that is outside of the oracle Database instance. The PGA stores control and data information fr a single background process terminates.One PGA ia applicable to one process only.
Oracle Database
As we discussed in before post in database architecture oracle database consists of two phases one os logical and other one is physical
- The control file is used to synchronize all oracle database activity
- The database files that store the database information that a organization needs in order to operate.
- The redo-log files are useful in recovering the data when the disk is failed or any network is failed.
We have three types of process:
- User process--Starts when a database user requests to connet to an oracle server
- Server process--Establishes the connection to an oracle Database instance when user process requests connection makes the connection for the user process
- Background process--These start when an oracle Database instance is started up
