CONCEPT筆記(一、Introduction to the Oracle Database)

1.Overview of Application Architecture
   Client/Server Architecture
   Client: initiates a request for an operation to be performed on the database server.
    Server: The server runs Oracle software and handles the functions required for concurrent, shared data access
  Multitier Architecture:
    Application Servers: It can serve as an interface between clients and multiple database servers, including providing an additional level of security.
   
2.Physical Database Structures
  Datafiles: contain all the database data
  Control Files: contains entries that specify the physical structure of the database
  Redo Log Files: The primary function of the redo log is to record all changes made to data. A redo log is made up of redo entries
  Archive Log Files:
  Parameter Files: spfile or pfile
  Alert and Trace Log Files:Each server and background process can write to an associated trace file
  Backup Files:User-managed backup and recovery requires you to actually restore backup files;Server-managed backup and recovery manages the backup process
 
3.Logical Database Structures
  Tablespaces:A database is divided into logical storage units called tablespaces
              The default is to create a smallfile tablespace, which is the traditional type of Oracle tablespace.Oracle also lets you create bigfile tablespaces,Oracle Database can now scale up to 8 exabytes in size
  Data Blocks:At the finest level of granularity, Oracle database data is stored in data blocks.standard block size is specified by the DB_BLOCK_SIZE.
  Extents:An extent is a specific number of contiguous data blocks
  Segments:A segment is a set of extents allocated for a certain logical structure.
           Data segment:Each nonclustered table has a data segment,For a partitioned table, each partition has a data segment
           Index segment:Each index has an index segment that stores all of its data.
           Temporary segment:When a SQL statement needs a temporary database area to complete execution and then returned to the system for future use.
           Rollback segment:The information in a rollback segment was used during database recovery for generating read-consistent database information and for rolling back uncommitted transactions for users.
           note:Because extents are allocated as needed, the extents of a segment may or may not be contiguous on disk
          
4.Schemas and Common Schema Objects
  Schemas:A schema is a collection of database objects
  Tables:Database tables hold all user-accessible data. Each table has columns and rows.
  Indexes:Indexes are optional structures associated with tables.an Oracle index provides an access path to table data.
          Changes to table data are automatically incorporated into all relevant indexes with complete transparency to the users.
  Views:Views are customized presentations of data in one or more tables or other views.Views do not actually contain data.
        Like tables, views can be queried, updated, inserted into, and deleted from, with some restrictionsAll operations performed on a view actually affect the base tables of the view.
  Clusters:Clusters are groups of one or more tables physically stored together
  Synonyms:A synonym is an alias for any table, view, materialized view, sequence, procedure,function, package, type, Java class schema object, user-defined object type, or another synonym.
           it requires no storage other than its definition in the data dictionary
          
5.Oracle Data Dictionary
  Data Dictionary:data dictionary is a set of tables and views that are used as a read-only reference about the database
 
6.Overview of the Oracle Instance
  The combination of the background processes and memory buffers is called an Oracle instance.
  Instance Memory Structures:
                              System Global Area: SGA is a shared memory region that contains data and control information for one Oracle instance.
                                                  Database Buffer Cache of the SGA:most recently used blocks of data
                                                  Redo Log Buffer of the SGA:redo entries—a log of changes made to the database
                                                  Shared Pool of the SGA: shared SQL areas / library cache / data dictorary cache and so on.
                                                  Statement Handles or Cursors:
                              Program Global Area: A PGA is created by Oracle when a server process is started
  Oracle Background Processes:
                              User Processes:User processes also manage communication with the server process,such as Enterprise Manager
                              Oracle Processes:Oracle creates server processes to handle requests from connected user processes
                                               In a dedicated server configuration, a server process handles requests for a single user process.
                                               In a shared server configuration lets many user processes share a small number of server processes.

7.Overview of Accessing the Database                              
  Network Connections:
                     Oracle Net Services is Oracle’s mechanism for interfacing with the communication
                     protocols used by the networks that facilitate distributed processing and distributed
                     databases.
  Overview of Oracle Utilities:
                     Data Pump Export and Import, SQL*Loader, and LogMiner