ORACLE12C Architecture (ii) ____oracle

5 Important Components

1. Services connected to database instances: How to work together in an Oracle system architecture;

2. Server process;

3. File system management;

4. Memory area management: especially the characteristics and functions of the system global Zone (Sga,systemglobal area);

5. Background Process 3 key architectures

1. Memory structure, process structure, storage structure

2.

3. The above figure shows that each Oracle server will contain two major components, Oracle instances, Oracle Databases (physical systems)

4. Oracle Servers, Oracle instances (instance), Oracle Databases (database) relationships

1. If Oracle is compared to a car, then the example is like the engine (core) of the car, and it is important to ensure that the instance is started before the Oracle is started, and the goods on the car are the database;

2. The relationship between an instance and a database is that a database can be loaded and opened by multiple instances, and instances can be loaded at any point in time to open a database; Oracle Instance System

1. Database startup, will automatically allocate the SGA (System global Area) memory, constitute the memory structure of Oracle, and then start a number of resident memory of the operating system process, has formed a oracel process structure, memory area and background process constitutes an Oracle instance;

2. Each operating Oracle database corresponds to an Oracle instance (or routine). Each instance allocates its own memory structure and process structure when it starts;

3. Oracle instance Tags: if there are multiple Oracle instances in the operating system (instance names cannot be the same), you can use ORACLE_SID (or use instance_name) to use this ambient property for annotations with the default usages; memory structure

1. Memory stores data dictionary information, about objects, logical structure, permissions and other metadata, buffered application data, SQL statements, Pl/sql and Java program data, and transactions and other information. In addition to these, the software code area and the program code area (PGA) are included

1.

2. Shared Area

(1). including the buffer zone, and data dictionary buffers, the database cache includes shared SQL, private SQL, shared Pl/sql area, and control structure area.

1. Private SQL Area: The private data used to hold each session associated with the execution of the SQL statement. In a dedicated server, a private SQL zone exists in the PGA, and in a shared server, a private SQL zone exists in a shared area;

2. Shared SQL area: When a user executes SQL, Oracle stores the text of the most recently executed SQL statement, the compiled parse tree, and the execution plan into the shared area. The value of the variable in the SQL statement is stored in the private SQL area. When the server executes the same SQL statement again, the server process will no longer parse the statement, but directly execute what already exists in the shared SQL zone;

3. Shared Pl/sql: Oracel The program unit into the shared Pl/sql area before executing a pl/sql statement, and the SQL statement within the program unit is placed in the SQL area, which is called directly from memory when the same program unit needs to be executed again, without having to access the disk again;

4). Structure Control Area: A section of memory area used for internal example, which holds the information of lock;

3. Database buffers

(1). This area is a high speed buffer area in the SGA to store data blocks, tables, and indexed databases that were recently read from the data file. When the user processes the query, the server process first looks for the required database from the database buffer and accesses the disk data in the buffer.

4. Redo Log Buffers

(1). When a user changes data through an SQL statement, the server process records the changes in the redo log buffer. Data can be recovered from this record after an unexpected database event

5. Large Pool

(1). Optional memory area. Large pools provide additional memory for use in operations that consume large amounts of memory;

6. Java Pool

(1). This place holds the Java text, the syntax analysis and so on information. If you want to install a Java VM, you must enable the Java pool;

7. Streams Pool

(1). This area is newly added by 10g. It is used to store information. The content it holds is shared. Using this pool to manage information is easier than capturing and managing messages;

8. Data dictionary Buffer

(1). It contains the structure of the database, user information and database tables, views and other information, as well as all tables and views of the nouns, and permissions and other information;

9. Program Global Area (PGA)

(1). Program Global Area: including session information, stack space, sorting area and cursor state;

1. Session information is stored in the session's permissions, role, session performance statistics and other information;

2. The stack space is stored in variables, arrays, and other information that belongs to the session;

3). The sort area is a dedicated space for sorting;

4. The cursor state is stored in the processing phase of the various cursors currently in use;

(2). When the user process is connected to Oracle, the server creates a session and allocates a PGA zone, which is used by a user process and cannot be shared;

1. For dedicated servers (a database connection corresponds to a dedicated server process), the PGA saves stack space information, session information, cursor status, and sort area.

2).