Oracle Database basics 2

1. Sga (oracle has a large memory block) Function
   1. Maintains various internal data structures that all processes need to access;
   2. Cache the data on the disk, and cache the data here before redoing the data to the disk;
   3. Save parsed SQL plans.
2. The two most common methods for Oracle server to process requests
   1. Dedicated server

• A new dedicated server will appear for each session, and there is a one-to-one ing between the session and the dedicated server.
• The client directly communicates with the dedicated server, and this service process receives and executes My SQL

1. Shared Server connection

• The client process does not directly communicate with the shared server.
• Multiple database sessions, requiring only a few processes/threads

1. TCP/IP connection
   1. The client software reads a tnsnames. ora file, which is a plain text configuration file. It is usually stored in [oracle_home] \ network \ admin. Based on the file configuration, the TNS connection string is mapped to useful information, that is, the host name (IP address) the port on the server that listens to the process, and the name of the service that connects to the database

Summary: oracle server consists of instances and databases.

 

I. Database startup

1. Nomout status

A) Search for the parameter file, create instances, allocate memory, and start background processes based on the settings in the parameter file.

B) For details, see the warning file (alter _ (sid ). log) through the admin \ orcl \ bdump directory, you can set the parameter query according to the background_dump. The parameter query can be based on the show parameter name or SELECT * from v $ parameter;

1. Mount status

A) read the control file and Password File

1. Open Status

A) read data files, log files, checkpoint information, etc.

B) Check whether the checkpoint count in the data file header is consistent with that in the control file.

 

It is important to look at the warning log file.