The oracle database is a centralized repository where data is stored. The Oracle database has a physical structure that is visible to the operating system and is made up of the Operating system’s files and logical structure that is recognized by the oracle server.
The user while requesting any request any information from oracle database, it first request the instance. Instances acts as an interface between user and database. And is the combination of shared global area and background processes of the oracle database. These instances are responsible for the fulfillment of user demand of information.
The user request the information from the server process which accepts IV request and creates an instance to locate
the needed or processed information from the data files and return it back to the user. These accepting, processing and delivering of the request of the user involved few oracle database components which also plays their role during the task.
Oracle Database System Architecture
The Oracle database system consists of a few components
1) Shared Pool: this component contains the library and dictionary cache with a few other important libraries.
2) Database Buffer Cache: This component contains the user’s data. The user can query their data from this component and in case the query is not present in this component then the server brings the data from dick to this component so that the user can execute its query.
3) Redo Log Buffer: The components contain the user’s operation entries such as INSERT, DELETE, CREATE TABLE, UPDATE, etc. The entries of the components are used to reconstruct the changes made in the database which guarantees the database recovery in case of any error or failure.
4) Large Pool: This field contains the information about the recovery manager utility whenever it is running. It provides RAM for server input-output operations, shared server, and parallel query data buffers. A large pool in oracle architecture is optional.
The above components are also referred to as the system global area(SGA) and are a part of the Instance Memory Component of the oracle architecture.
5) Log Writer Background Process (LGWR): this component writes the redo entries from redo log buffers when the user executes the commit statement or the buffer exceeds 1/3rd of the redo log buffers.
6) Database Writer Background Process(DBWR): This component will write all the dirty blocks whenever checkpoints tell them to do it.
7) Checkpoint Background Process(CKPT): This component signals the database writes to write all dirty blocks into the disk.
8) Recovery Background process(RECO): This component is used to recover from database failure in distributes database system.
9) LOCK Background Process(LCKN): This component is used in the situation when multiple instances access a single database.
10) Program Monitor Background process(PMON): This component will clean the reminding memory allocation that was allocated to the user when the user disconnects the communication link.
11) System Monitor background Process (SMON): This component synchronizes the data files, log files, etc before the user starts the database.
