Oracle Database
一：An Oracle database:Consists of three file types
Control Data files
Redo files
log files
二：Physical Structure：determined by the operating system files
三：Memory Structure
1.System Global Area (SGA): Allocated at instance
startup, and is a fundamental component of an
Oracle Instance
2.Program Global Area (PGA): Allocated when the
server process is started
System Global Area (SGA)
SGA is dynamic and sized using SGA_MAX_SIZE.
The SGA consists of several memory structures:
– Shared pool
– Database buffer cache
– Redo log buffer
– Other structures (e.g. lock and latch management,
statistical data)
There are two optional memory structures that can
be configured within the SGA:
– Large pool
– Java pool
Shared Pool
Sized by the parameter ：SHARED_POOL_SIZE.
The shared pool is used to store the most recently
executed SQL statements and the most recently used
data definitions.
It consists of two key performance-related memory
structures:
– Library cache：
Stores information about the most recently used SQL and PL/SQL statements、
– Data dictionary cache
a collection of the most recently used definitions in the database.
Database Buffer Cache
Sized by the parameter ：DB_BLOCK_SIZE
shrink [ʃriŋk] 收縮 using ALTER SYSTEM.
ALTER SYSTEM SET DB_CACHE_SIZE = 96M;
stores copies of data blocks that have been retrieved from the data files.
Consists of independent sub-caches:
– DB_CACHE_SIZE
– DB_KEEP_CACHE_SIZE
– DB_RECYCLE_CACHE_SIZE
Redo Log Buffer Cache： Its primary purpose is recovery.
Size is defined by LOG_BUFFER.
records all changes made to the database data blocks.
Other structures
ALTER SYSTEM SET LARGE_POOL_SIZE = 64M;
Large Pool: It relieves減輕, the burden重載placed on the shared pool.
Java Pool: parsing requirements for Java commands. JAVA_POOL_SIZE
Program Global Area (PGA)
The PGA is memory reserved保留for each user process that connects to an Oracle database.
Process Structure
is a program that depending on its type can request information, execute a series of
steps, or perform a specific task.
1. User process: Started at the time a database user requests connection to the Oracle server
* It must first establish a connection.
* It does not interact相互作用directly with the Oracle server.
2. Server process: Connects to the Oracle Instance and is started when a user establishes a session.
*It fulfills完成 calls generated產生 and returns results.
*Can be dedicated獻出 or shared server.
3. Background process: Available when an Oracle instance is started
the physical and memory structures is maintained and enforced by Oracle’s
background processes.
Mandatory background processes
DBWn (Database Writer) PMON (Process Monitor) CKPT(Checkpoint)
LGWR( Log Writer ) SMON (System Monitor) RECO(Archiver)
Logical Structure
A hierarchy ['haiərɑ:ki] 等級制度exists in this structure that consists of tablespaces, segments, extents, and blocks.