Shulou(Shulou.com)05/31 Report--

This article introduces the knowledge of "how to understand Oracle architecture". Many people will encounter this dilemma in the operation of actual cases, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

1. From one point of view, the database can be divided into database software and database files. By database, we usually refer to database files. Usually, the database software is installed on the server and the database files are stored in storage.

two。 From another point of view, the database can be divided into database files and database instances. Here, the database file can be understood as static and the example as dynamic. Users change the data through dynamic instances, and then write the changed data into a static database file.

3. Database file

The location of the database file is in the $ORACLE_BASE/oradata/ {db_unique_name} / directory. There are three kinds of files.

(1) Control file (.ctl)

(2) Log file (.log)

(3) data file (.dbf)

4. Database instance

The database instance is divided into memory and processes. Just like when every software runs, it allocates some space to itself in the memory of the server. When Oracle executes startup in sqlplus, it actually opens the instance, which is equivalent to opening the database software, that is, opening memory and processes. Both memory and processes are moved to the server's memory.

5. The memory structure of the database includes: SGA (system global area, shared, where sharing refers to all the space of SGA, which can be accessed by oracle processes) and PGA (process global area, non-shared), both of which are in memory. As the name implies, the process is stored in the process global area.

(1) the system global area (SGA) includes the following:

(1) shared pool

(2) flow pool

(3) JAVA pool

(4) large pool

(5) Database buffer → database write process

(6) redo log buffer → log writing process

Here, shared pools and database buffers are prone to problems.

(2) the process global area (PGA) includes the following two major processes:

Background process and foreground process. The background process here is the official name, and the foreground process refers to the server process. Here, I call the process of the database itself a background process, and each external connection to the database is regarded as a foreground process, which is easier to understand. Each process (foreground and background) has its own space, which is in the PGA. What we need to pay attention to is the PGA space consumed by the foreground process, because the background process is not very problematic.

6. ORACLE background process

Oracle's SGA has six chunks, PGA has five processes, and there are three kinds of data files.

Five of the major processes are:

(1) CKPT (checkpoint process) → control file

(2) SMON (system monitoring process)

(3) PMON (process monitoring process)

(4) DBWN (database writing process) → data file

(5) LGWR (log writing process) → log file

7. Control file

There are two messages in the control file.

(1) the physical structure information of the whole database is recorded in the control file. These physical structures include how many data files, log files, etc., and where these files are stored in the entire database.

(2) some current running status information of the database. For example, which data files are online, which data files are offline, which log file Oracle is using, and what is wrong with the log file.

8. Log file

Log files are also called redo log files (redo log), which means that all changes made by Oracle to the data are stored in the log file in the form of logs. All the changes of each block in the database are recorded in the log file.

That's all for "how to understand Oracle Architecture". Thank you for reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.