Search notes:

V$EVENT_NAME: Wait Classes

select
   count(*) cnt,
   wait_class,
   wait_class#
from
   v$event_name
group by
   wait_class#,
   wait_class
order by
   count(*) desc;
--
--     CNT WAIT_CLASS       WAIT_CLASS#
---------- ---------------- -----------
--    1647 Other                      0
--     170 Idle                       6
--      80 User I/O                   8
--      78 Cluster                   11
--      75 Concurrency                4
--      61 Administrative             3
--      43 System I/O                 9
--      29 Network                    7
--      29 Configuration              2
--      21 Application                1
--      12 Scheduler                 10
--      11 Queueing                  12
--       7 Commit                     5

Idle	The process has nothing todo, typically because it waits for the client to send a new SQL statement to process.
User I/O	I/O for user queries, including SMON and MMON. Compare with System I/O.
Cluster	RAC
Concurrency	Cannot(?) be tuned - compare with Configuration. k
Administrative	Caused by a privileged user (
System I/O	I/O performed by background processes (like LGWR, DBWR, ARCH, RFS), excluding SMON and MMON. Compare with User I/O.
Network	High wait times indicate congestion or high latency in the network
Configuration	Waits whose wait time can probably be greatly reduced when Oracle is properly tuned. Compare with Concurrency.
Application	Waits that are caused by the application (client?) themselves (explicit locking, DDL …)jk
Scheduler	Resource manager
Commit
Other

Sessions that are waiting on an Idle event are not recorded in v$active_session_history

Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 8 attempt to write a readonly database in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php:78 Stack trace: #0 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(78): PDOStatement->execute(Array) #1 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(30): insert_webrequest_('/notes/developm...', 1788537157, '216.73.217.21', 'Mozilla/5.0 App...', NULL) #2 /home/httpd/vhosts/renenyffenegger.ch/httpsdocs/notes/development/databases/Oracle/installed/dynamic-performance-views/event_name/wait_classes(88): insert_webrequest() #3 {main} thrown in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php on line 78

V$EVENT_NAME: Wait Classes

See also