What is an edition?

Question

Server is 11.1.0.7 on Linux/x86. I noticed processes sometimes holding an "edition lock" on object ORA$BASE. The
V$LOCK_TYPE table says the following: "Prevent Dropping an edition in use<br />". To make things even more confusing,
there is a very well hidden view named '_CURRENT_EDITION_OBJECT'. Here is the text:
<code>select text
from dba_views where view_name = '_CURRENT_EDITION_OBJ';
TEXT
select o."OBJ#",o."DATAOBJ#",o."OWNER#",o."NAME",o."NAMESPACE",o."SUBNAME",o."TY<br /><br /><br />PE#",o."CTIME",o."MTIME",o."STIME",o."STATUS",o."REMOTEOWNER",o."LINKNAME",o."FL<br /><br /><br />AGS",o."OID$",o."SPARE1",o."SPARE2",o."SPARE3",o."SPARE4",o."SPARE5",o."SPARE6",
o.spare3,
case when (o.type# not in (4,5,7,8,9,10,11,12,13,14,22,87) or
bitand(u.spare1, 16) = 0) then
null
when (u.type# = 2) then
(select eo.name from obj$ eo where eo.obj# = u.spare2)
else
TEXT
'ORA$BASE'
end
from obj$ o, user$ u
where o.owner# = u.user#
and ( /* non-versionable object */
( o.type#
not in (4,5,7,8,9,10,11,12,13,14,22,87,88)
or bitand(u.spare1, 16) = 0)
/* versionable object visible in current edition
or ( o.type# in (4,5,7,8,9,10,11,12,13,14,22,87)
and ( (u.type# &lt;&gt; 2 and
sys_context('userenv', 'current_edition_name')
= 'ORA$BASE')
TEXT
or (u.type#
= 2 and
u.spare2 = sys_context('userenv', 'current_edition_id'))
or exists (select 1 from obj$ o2, user$ u2
where o2.type#
= 88
and o2.dataobj# = o.obj#
and o2.owner# = u2.user#
and u2.type# = 2
and u2.spare2 =
sys_context('userenv',
'current_edition_id'))
TEXT
) </code>
OK. Here are the questions:
What is the purpose of those "edition objects"? I figured out that it is about sys_context, but it's still unclear? The "CURRENT_EDITION_ID" option is not documented as a legal option for the SYS_CONTEXT function. What are the
users of type# 2? I don't have any in my databases. Users of type#=0 are roles, users of type#=1 are the normal lusers.
What in the world are the users of type#=2? Last but not least, what is protected by locks of the type AE? Did I mention
that there is no documentation about this on Metalink? Nada, nil, zilch. On version 10, "editions" are not recognized:
SQL&gt; select sys_context('userenv','current_edition_id') from dual;
select sys_context('userenv','current_edition_id') from dual
ERROR at line 1:
ORA-02003: invalid USERENV parameter
Version 11 recognizes the arguments as correct:
Connected.
SQL&gt; select sys_context('userenv','current_edition_id') from dual;
SYS_CONTEXT('USERENV','CURRENT_EDITION_ID')
99
I am an oracle beginner with only a few months of experience. Please, gurus, help me with my questions.

Answer 1

Niall, you got me. The "beginner clause" at the end was a joke. I noticed that people are always trying to help beginners, so I decided that
it would be beneficial to be one. After posting this, I had a phone conversation with a friend in the know who told me that this is a part of the "rolling
upgrade" feature. Essentially, in order to upgrade one node to the new version whilst allowing the other nodes to run the old version of the
dictionary, you need to have both versions running concurrently. How can you tell between the versions ("editions") of the data dictionary?
You introduce "edition objects" and add an argument to sys_context function to enable it to discern among the different editions. That can be
guessed from the ML document 565413.1 which explains how DBA_SOURCE view was altered to include the sys_context function.
Also, thanks to Maxim Demenko, I learned that Dan Morgan has partly documented this feature at: http://www.psoug.org/reference/editions.html
Thanks to everybody.