"Reprint" Oracle architecture diagram

1. Several important Oracle Terminology
To learn about Oracle's architecture, there are a few important terms to understand: Oracle server, oracle instance, Oracle database.
Oracle Server: Oracle server, comprised of Oracle instances and Oracle databases.
Oracle Instances: Oracle instance, which is the first stage of Oracle startup, is composed of a series of background processes and a shared memory SGA based on the parameter file.
Oracle Database: Oracle database, which is made up of all the physical files of Oracle. The most critical of these are: control files, data files, redo log files, and so on.
Oracle instances interact with Oracle databases, and Oracle instances perform various operations on the database to provide storage and retrieval services to the database.

2. Oracle Overall architecture
Oracle server is comprised of Oracle instance and Oracle database. Oracle instance is also made up of background processes and shared memory, so the structure of Oracle includesMemory StructureAndProcess Structure, and Oracle database has physical files, so the Oracle architecture also containsStorage Structure。

The following is an overview of Oracle Memory Architecture, Oracle process architecture, and Oracle storage architecture, giving us a preliminary idea of Oracle.
3. Oracle Memory Architecture
In general, Oracle's memory consists of two main parts: the PGA and the SGA, as shown in the following structure:


Either the server process or the background process, they have their own process-private memory space, the PGA, and the SGA is used for all background inter-process shared access.
The PGA assigned to the server process is divided into several specific sections according to its function. Follow-up blog to further specific discussion.
The SGA is divided into 6 sections in the oracle10g, as shown in. The following outlines their effects:
1)Shared Pool(Shared Pool):
The main function is to improve the efficiency of SQL statements and PL/SQL statements, to cache the executed statements, execute the plan, the code blocks of the PL/n statements, the execution code, and so on (this part is calledLibrary CacheAnd in compiling SQL, the PL/SQL statement is a reference to the data dictionary information (this part is calledDictionary CacheOrRow Cache)。 is one of the most important parts of the SGA.
2)Database Buffer Cache(Database buffer):
The primary role is to cache blocks of data that have been read, and all modifications to the data in the Oracle database are performed in buffer cache. Because all operations must first read the data blocks on the physical file into the buffer cache, you can perform various operations. Buffer cache is the largest area of memory in the SGA and is one of the most important parts of the SGA.
3)Redo Log Buffer(Redo log buffer):
The redo log record generated by the cache, and the log write background process writes the records in log buffer to disk. is one of the most important parts of the SGA.
4) Large pool (Big pond):
An optional memory pool whose primary role is to share the pressure of the shared pool. In some cases, such as backup recovery, if no large pool is allocated, memory is allocated from the shared pool, which increases the burden on the shared pool.
5) Java Pool (Java pools):
For use with Java programs.
6) stream Pool (stream pools):
The database in which the stream works is the area of memory used.
4. Oracle Process Architecture
Oracle's processes are mainly background processes and server process (in fact, in the strict sense of Linux, server process also belongs to the background process). Background processes are primarily for the maintenance and operation of Oracle database processes, while the server process primarily handles user requests:

When a user process accesses Oracle Instacne through a listener, it touches a server process process to process the request process for that user process. Background processes generally include: LGWR, Dbwn, ARCn, CKPT, Smon, Pmon and so on.
1)Dbwn(written by database writer):
The main function is to write the modified buffer cache to the physical disk according to certain conditions.
2)LGWR(log writer, Journal write):
The main function is to write the redo log record in log buffer to the online redo log file according to certain conditions.
3)CKPT(checkpoint, checkpoint process):
The primary function is to write the checkpoint location (checkpoint position) to the head of the control file and data file.
4)Smon(System Monitor, monitoring process):
The main role is to determine when the database starts, the last time the instance is shut down properly, and if it is off gracefully, the process instance resumes. In addition, the connected spaces can be merged.
5)Pmon(Process Monitor, progress monitoring):
Monitoring server process, if the server process shuts down gracefully, Pmon is responsible for cleaning up the various resources it occupies.
5. Oracle Storage Architecture
The storage structure is the constituent structure of the physical file, and the physical files that Oracle involves are as follows:

Figure 2:

The control files, data files, redo log files are indispensable key files:
1)Control File(Control file):
Contains information about the physical structure of the database, such as the location of various files, the running state of the current database, and so on. It is important that the database instance cannot be started when it is lost.
2)datafile(Data file):
The file that holds the data.
3)Online redo log file(Online redo log file):
The file that holds the redo log. Maintains database consistency and is used for database recovery.