Concepts of databases, service names, and instances in Oracle

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An instance is the name used to manage the memory structure of relevant databases (consisting of SGA, PGA, server processes, user processes, and background processes)

A database is a file (data file, log file, control file, etc.) on the actual disk. It stores data, but its data is operated by the corresponding instance.

The service name is the name published to the outside world. It is the network listening service.

In fact, in our traditional concept, databases are collectively referred to as names. In Oracle, you can think of "databases" as a big concept, but also a small concept.

　　

1. Several databases can be installed in an Oracle database system at the same time. Each database corresponds to a unique

One instance, except for the OPS System, multiple instances can operate on one database at the same time. This is called a parallel service.

Tool

2. It is just a name. Sid is instance_name, and service_names is mainly used in the listener,

For convenience, some are for the continuation of traditional habits, and some are for more convenient use.

3. net easy config is used to manipulate host strings and serve clients.

One database can publish multiple service names (service_names)

A client can also use multiple host strings to connect to the same database server.

4. Multiple Oracle databases (small concept) can be installed on one OS. Each database can publish multiple servers.

The service names are all implemented through init. ora and listener. ora.

　　

Today, we were lucky to have met the experts.

I have to hurry up.

Then ask again:

In your explanation, the host string, Database Service name, and database alias should be the same concept?

Not the same

Service_names is the external service name used by the server. Multiple external servers can be set in one database.

Service name for different purposes

The host string is mainly used in SQL * Plus and is used on the client,

The "database alias" is commonly used to connect to Oracle servers using some development tools.

The service name of data source when ODBC is configured,

They all point to a small text section in the client tnsnames. ora file.

I almost understood it.

But I also want to ask:

1. In SQL/plus login, use user/pwd @ ***. So what is this? Yes host word

String or service name?

2. When setting ODBC, must the user and password be a valid user and password in Oracle?

3. If you want to purchase oracle from an oracle agent, you are charged for the number of users.

Then, this "user" follows us in Oracle through the create user username identified

Is a user created by password a concept? If not, what are their differences?

Also, what mechanism does orcle use to control the maximum number of users? If I buy eight users, I

Can I open 12 users?

Can you email me?

　　

1. host string

2. Yes, but it is OK if you do not enter the ODBC name. You can also give it again when referencing the ODBC name.

3. No. "Number of users" indicates the number of concurrent users.

(I understand the number of processes that access the same memory address at the same time)

It's okay to buy eight users and create dozens or even hundreds of users, as long as the peak value does not reach the number of concurrent users.

(The number of users here is not the kind of user set up in Oracle, it should be the number of processes)

(Multiple machines, each Oracle internal user calls multiple times and starts multiple processes)