Oracle Database
A collection of Data files, Control Files, And Redo Logs
Oracle Instance
It is comprised of Memory and Background
... [Show More] Processes
Oracle Server
An Instance associated with a database (can be more than one instance per server e.g. Real Application Clusters)
Three major sections of Oracle Database Architecture
Storage, Memory (SGA), and Processes
Storage: main components
Data Files, Control Files, Online Redo Logs, and Archive Logs
Memory: main components
System Global Area (SGA), Shared Pool, Database Buffer Cache, Redo Log Buffer, Large Pool, Java Pool, and Program Global Area
Processes: main components
SMON (system monitor), PMON (process monitor), DBWO (database writer), CKPT (checkpoint process), LGWR (redo log buffer), ARCO (redo log archiver), Least Recently Used Algorithm (LRU)
Data Files
storage
Stores data
Type of data stored:
tables, indexes, undo files, temporary files, views
Control Files
storage
Stores the structure of the database
Type of data stored:
database name, when the database was created, path names for all the data files, checkpoint information
Online Redo Logs
storage
Stores changes to the database
Stored in groups (Multiplexed)
Log checkpoint and switch starts writing to another Online Redo Log
Type of data stored:
Data Manipulation Language
&
Data Definition Language
Archive Logs
storage
If the option is chosen (not default), when the Online Redo Logs are filled it is copied to Archive Redo Logs
System Global Area (SGA)
Memory
The SGA is a read/write group of shared memory structures that contain data and control information for one Oracle Database instance. The SGA is shared by all server and background processes.
It also just Oracle's name for memory
Shared Pool
memory
Purpose is to reduce Parsing. Contains two main components:
Library Cache:
-Store the text of the SQL statement.
-Stores the compiled version of the SQL statement (Meta Code).
-Execution Plan of how the Oracle Optimizer will retrieve queried rows .parse information for SQL statements executing against the database.
Dictionary Cache:
Contains Data Dictionary information that has been recently used
Data such as:
datafile names, table descriptions, user privileges
Database Buffer Cache
Memory
Allows obtaining and changing data. The buffer cache stores data blocks that contain row data that has been selected or updated recently.
Divided into Oracle Data Blocks. Four major types of Data Blocks, indexes, undo files, temporary files
Redo Log Buffer
Memory
Every process that makes a change to the database must write an entry to the redo log in order to allow Oracle to recover the change.
Large Pool
Memory
Optional Memory that provides relieves the memory burden on the Shared Pool
Stores:
Oracle backup and restore processes used by the (RMAN) Process
It avoids the performance overhead caused by shrinking the shared SQL cache and frees up the shared pool.
Java Pool
Memory
Required if Java is installed and in use for Oracle Java Virtual Machine.
Used for memory allocation to parse Java commands and to store data associated with Java commands
Program Global Area
Memory
A PGA is a non-shared memory region that contains data and control information used exclusively for an Oracle process.
One PGA exists for each server process and background process.
GENO (general task execution process)
Processes
Takes what is in memory and writes to the appropriate storage space
SMON (system monitor)
Processes
All background process talk to SMON and SMON talks back. When there is an instance crash SMON will perform crash recovery. by applying Online Redo Logs to committed datafiles.
PMON (process monitor)
Processes
Monitors processes, Detects dead locks, and Cleans up after aborted processes
DBWn (database writer)
Processes
Writes the contents of Dirty Blocks in Buffer Cache to and from data files.
Does deferred writes
CKPT (checkpoint process)
Processes
Blocks can keep getting updated and stay in memory forever. There needs to be a mechanism that can force the database writer to write the updated committed blocks to their appropriate data files.
Checkpoints can be forced by a command or a parameter can dictate then the occur
This does not write directly. It calls upon the DBWn and the LGWR as necessary
LGWR (redo log Writer)
Processes
Writes the data being stored in the Redo Log Buffer to the current Online Redo Log. Also does deferred writes.
ARCn (redo log archiver)
Processes
When Redo Log Files fill up, they are individually written to the Archived Redo Log
User Process
Starts when a database user requests to connect to an Oracle Server. Can be done through SQLPlus or another application. Does not directly interact with the oracle server
Database Listener
Runs on the database server computer. It receives incoming client connection requests and manages the traffic of these requests to the database server
Server Process
Establishes the connection to an Oracle Instance when a User Process requests a connection. It acts as the go between for the User Process and the Oracle Instance
Least Recently Used Algorithm (LRU)
Memory
As block get popular they go to the left (Stay in Memory), block not used go to Storage. Applied to both the Database Buffer Cache and Shared Pool. Allows for quicker memory
What is a Storage
Typically a series of Hard Disk Drives that store data
What is Memory
Is used to store information fast and efficiently for interactions between oracle processes and storage.
What is Processes
A mechanism that can execute a series of steps. The process of accomplishing a job or task
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