SQL> show parameter processes;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
aq_tm_processes integer 0
db_writer_processes integer 2
gcs_server_processes integer 0
global_txn_processes integer 1
job_queue_processes integer 0
log_archive_max_processes integer 5
processes integer 150
SQL> show parameter sessions;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
java_max_sessionspace_size integer 0
java_soft_sessionspace_limit integer 0
license_max_sessions integer 0
license_sessions_warning integer 0
sessions integer 256
shared_server_sessions integer
SQL> alter system set processes = 300 scope = spfile;
System altered.
SQL> alter system set processes = 1000 scope = spfile;
System altered.
SQL> alter system set sessions=1100 scope=spfile;
System altered.
SQL> shutdown immshutdown immediate;
SP2-0717: illegal SHUTDOWN option
SQL>
SQL>
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 1.3429E+10 bytes
Fixed Size 2217992 bytes
Variable Size 8589936632 bytes
Database Buffers 4831838208 bytes
Redo Buffers 4661248 bytes
Database mounted.
Database opened.
SQL>
The number of ORACLE connections (sessions) is related to the number of processes in its parameter file (process), and their relationship is as follows:
sessions=(1.1*process+5)
Extract (2)
Query the number of connections in the current process of the database:
select count(*) from v$process;
View the number of connections for the current session of the database:
elect count(*) from v$session;
Check the number of concurrent connections to the database:
select count(*) from v$session where status='ACTIVE';
View the session status established by the current database:
select sid,serial#,username,program,machine,status from v$session;
Query the maximum number of connections allowed to the database:
select value from v$parameter where name = 'processes';
Or: show parameter processes;
Modify the maximum number of connections allowed by the database:
alter system set processes = 300 scope = spfile;
(需要重启数据库才能实现连接数的修改)
重启数据库：
shutdown immediate;
startup;
查看当前有哪些用户正在使用数据：
select osuser,a.username,cpu_time/executions/1000000||'s',sql_fulltext,machine
from v$session a,v$sqlarea b
where a.sql_address = b.address
order by cpu_time/executions desc;
备注：UNIX 1个用户session对应一个操作系统process，而Windows体现在线程。
启动oracle
su - oracle
sqlplus system/pwd as sysdba //进入sql
startup //启动数据库
lsnrctl start //启动监听
sqlplus "/as sysdba"
shutdown immediate;
startup mount;
alter database open;