View and modify connections in Oracle

1. query the number of connections to the current process of the database:
Select count (*) from V $ process;
2. view the number of connections in the current session of the database:
Elect count (*) from V $ session;

3. view the number of concurrent connections of the database:
Select count (*) from V $ session where status = 'active ';
4. view the session information of the current database:
Select Sid, serial #, username, program, machine, status from V $ session;
5. query the maximum number of connections allowed by the database:
Select value from V $ parameter where name = 'processs ';
Or command: Show parameter processes;
6. Modify the maximum number of connections allowed by the database:
Alter system set processses = 300 scope = spfile;
(You must restart the database to modify the number of connections.)

Restart the database:
SQL> shutdown immediate;
SQL> startup;
Check which users are using the data:
SQL> select osuser, A. username, cpu_time/executions/1000000 |'s ', SQL _fulltext, Machine
SQL> from V $ session A, V $ sqlarea B
SQL> where a. SQL _address = B. Address
SQL> order by cpu_time/executions DESC;
Note:One session of a Unix user corresponds to an operating system process, while windows is embodied in a thread.

Start Oracle
Su-Oracle
SQL> sqlplus system/pwd as sysdba // enter SQL
SQL> startup // start the database
SQL> LSNRCTL start // start the listener

sqlplus "/As sysdba"
SQL> shutdown immediate; // close the database
SQL> startup Mount;
SQL> alter database open;