How to check the maximum number of allowed connections to an Oracle database?
SqlOracleSql Problem Overview
What's the best way, using SQL, to check the maximum number of connections that is allowed for an Oracle database? In the end, I would like to show the current number of sessions and the total number allowed, e.g. "Currently, 23 out of 80 connections are used".
Sql Solutions
Solution 1 - Sql
There are a few different limits that might come in to play in determining the number of connections an Oracle database supports. The simplest approach would be to use the SESSIONS parameter and V$SESSION, i.e.
The number of sessions the database was configured to allow
SELECT name, value
FROM v$parameter
WHERE name = 'sessions'
The number of sessions currently active
SELECT COUNT(*)
FROM v$session
As I said, though, there are other potential limits both at the database level and at the operating system level and depending on whether shared server has been configured. If shared server is ignored, you may well hit the limit of the PROCESSES parameter before you hit the limit of the SESSIONS parameter. And you may hit operating system limits because each session requires a certain amount of RAM.
Solution 2 - Sql
The sessions parameter is derived from the processes parameter and changes accordingly when you change the number of max processes. See the Oracle docs for further info.
To get only the info about the sessions:
select current_utilization, limit_value
from v$resource_limit
where resource_name='sessions';
CURRENT_UTILIZATION LIMIT_VALUE
110 792
Try this to show info about both:
select resource_name, current_utilization, max_utilization, limit_value
from v$resource_limit
where resource_name in ('sessions', 'processes');
RESOURCE_NAME CURRENT_UTILIZATION MAX_UTILIZATION LIMIT_VALUE
processes 96 309 500 sessions 104 323 792
Solution 3 - Sql
I thought this would work, based on this source.
SELECT
'Currently, '
|| (SELECT COUNT(*) FROM V$SESSION)
|| ' out of '
|| DECODE(VL.SESSIONS_MAX,0,'unlimited',VL.SESSIONS_MAX)
|| ' connections are used.' AS USAGE_MESSAGE
FROM
V$LICENSE VL
However, Justin Cave is right. This query gives better results:
SELECT
'Currently, '
|| (SELECT COUNT(*) FROM V$SESSION)
|| ' out of '
|| VP.VALUE
|| ' connections are used.' AS USAGE_MESSAGE
FROM
V$PARAMETER VP
WHERE VP.NAME = 'sessions'
Solution 4 - Sql
Note: this only answers part of the question.
If you just want to know the maximum number of sessions allowed, then you can execute in sqlplus, as sysdba:
SQL> show parameter sessions
This gives you an output like:
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
java_max_sessionspace_size integer 0
java_soft_sessionspace_limit integer 0
license_max_sessions integer 0
license_sessions_warning integer 0
sessions integer 248
shared_server_sessions integer
The sessions parameter is the one what you want.
Solution 5 - Sql
Use gv$session for RAC, if you want get the total number of session across the cluster.
Solution 6 - Sql
v$resource_limit view is so interesting for me in order to glance oracle sessions,processes..:
https://bbdd-error.blogspot.com.es/2017/09/check-sessions-and-processes-limit-in.html
Solution 7 - Sql
select count(*),sum(decode(status, 'ACTIVE',1,0)) from v$session where type= 'USER'