Oracle expert Advanced Programming Study Notes (2)

Oracle expert Advanced Programming Study Notes (2)

Three main components of Oracle architecture:
1. File: five files that constitute the database instance (parameter files, control files, data files, temporary data files, and redo log files)
2. system global area (SGA): Java pool, Shared Pool, etc.
3. Physical Processes and threads: three different types of processes (server processes, backgroud processes in the background, and slave processes) are run on the database)

Glossary:
Database: a collection of physical operating system files
Instance: A group of Oracle processes and SGA
Relationship:
One database can be mounted by multiple instances and open
The instance can load and open a separate database in a timely manner. The databases opened and loaded by the instance do not need to be the same at startup.

File:
1. parameter file:
Tnsnames. ora, listener. ora, sqlnet. ora, Protocol. ora, names. ora, sman. ora, LDAP. ora
(Refer to "Oracle Net Administrator Guide ")
$ ORACLE_HOME/dbs/INT <oracle_sid>. ora: contains a series of variable names and value pairs.
Such:
Db_name = "wmdb"
DB _ block_size = 8192
Control_files = ("C: \ oradata \ control01.ctl", "C: \ oradata \ control02.ctl ")
...
Some parameters that are not described in the Oracle document start with an underscore
Except for setting the parameter _ trace_files_public = true in the development environment, it is recommended that you do not change other unspecified parameters.

2. data file:
Database --> tablespace --> segment section --> extent extended area --> Block
1) The database is composed of one or more tablespaces.
2) a tablespace is composed of one or more data files. A tablespace has one or more segments.
3) a segment (table, index, and so on) is composed of multiple extended areas. The segment exists in the tablespace, but there are multiple data files in the tablespace.
4) an extended area is some contiguous blocks allocated on the disk. an extended area is in a tablespace and is always a single file in the tablespace.
5) a block is the smallest allocation unit and I/O unit in the database. Its size is fixed during database creation.

3. Temporary Files
When the memory is insufficient to store intermediate results (sets) for a large-scale sorting operation, Oracle uses temporary files to store them, and permanent data, such as tables or indexes, is not stored in temporary files, however, contents of temporary tables or temporary indexes may be stored in temporary files.

We recommend that you use local temporary tablespace management to configure databases ???, Example
Create temporary tablespace temp
Tempfile 'C: \ oracle \ oradata \ Walter \ Temp. dbf'
Size 5 m
Extent management local
Uniform size 64 K

4. Control File
A very small file, usually 64 MB, contains the directories of other files required by Oracle
Data File init <Sid>. Ora tells the instance Control File Location
The control file informs the instance of the location of the database and online redo log files.
The control file also provides other information to Oracle, such as checkpoints, database names, timestamps of database creation, and redo archiving logs.

5. redo log files
The transaction log of the data, which is used only when the data is recovered.
1) Online redo log
2) archive redo logs

Memory Structure
1. SGA (system global area)
2. PGA (process Global Area)
3. UGA (User Global Area)