Shulou(Shulou.com)06/01 Report--

Oracle has many names, and many people are easy to get confused. Through the presentation at all levels, we will understand them from the perspective of vision and process, rather than only through concepts, so it will be easier to know them and understand the differences between them.

DB_NAME

The database name, which cannot exceed 8 characters in length, is recorded in datafile, redolog, and control file.

In this section, you can view the storage mode through bbed. Let's take the system01.dbf data file as an example.

Here we see that the data file header only stores the database name of Oracle in a position of eight characters, which is why we say that the length cannot exceed 8 characters. Dump can see the following:

Starting with the 32-bit character, the stored data file, which is given to the location according to the @ 32 feedback from the first picture O, can also be verified by the following statement

DBID

DBID is calculated by DB_NAME combined with algorithm when the database is created, and consists of a string of numbers.

It exists in datafile and control file to indicate the attribution of data files, so DBID is unique. For different databases, DB_NAME can be the same, but DBID must be unique.

Let's take the system01.dbf in the above figure as an example, which is stored in the header of the data file in reverse order.

We can still verify it with the to_char command

DB_UNIQUE_NAME

In DataGuard, the master and slave libraries have the same DB_NAME, and in order to distinguish, there must be different DB_UNIQUE_NAME

SID & INSTANCE_NAME

If you want to get the instance name in the operating system, you must use ORACLE_SID. InitSID.ora and orapwSID files should be consistent with ORACLE_SID.

The database looks for spfile according to ORACLE_SID, and then starts the instance with ORACLE_SID as INSTANCE_NAME, so its associated process name is also the name of ORACLE_SID.

This name can be consistent with or inconsistent with the database name, and there is generally little difference for ease of distinction.

When you build the library manually, the DB_NAME in the parameter file is read, and then the control file, data file, and redo log file are written during the creation process, so the database name and instance name can be inconsistent.

SERVICE_NAME

The connection between the database and the client is the name of the service used, which is the same as DB_UNIQUE_NAME by default, or multiple SERVICE_NAME can be added for the service.

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