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'Event Group Latch'

From: Connor McDonald <hamcdc_at_yahoo.co.uk>
Date: Wed, 28 Mar 2001 01:10:15 -0800
Message-ID: <F001.002D9C75.20010327235546@fatcity.com>

Tom Kyte (asktom.oracle.com) kindly posted me a reply to my question on the above latch. For anyone interested, the description is below

Cheers
Connor

Usage
This latch is used during the following operations :  An "alter system set events.." command.  During process startup where the process copies the events stored in the
 System event group to its Process event group.

Event Groups

Events are considered to exist in either the process, session or system group.
The differences are outlined below :

System Group
The event tree is built in the SGA and is derived from the settings of the
instance parameter "event". It can also be modified by using the command "alter
system set events...".

Process Group
These are initialised at process startup time via the instance parameter
"event". When the process starts up we copy the event tree that we have stored
in the System Group. The event tree is built in the PGA. Session Group
These are events that are modified dynamically via the "alter session" command.
When we perform event checking we check the session group events before those of
the process group. The event tree is built in the UGA.


Connor McDonald
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