CREATE INDEX IND_T2_C1_C2 ON T2 (C1, C2);

The above index definition did NOT help avoid the TM enqueue and the resulting deadlock on Oracle Database 11.2.0.2, so what you stated still appears to be correct for the latest version of Oracle Database.

I came to this old thread from your latest blog post “Insert Error on Oracle 11g but Not on 10g”. In addition to what Jonathan wrote above “it’s not commonly realised that the “foreign key index” doesn’t have to be an exact match for the foreign key; it merely has to start with the foreign key columns (which can be in any order) to avoid the locking issue”, he also mentions in his book Practical Oracle 8i to compress this index to save space (which will reduce number of Index Blocks so as to reduce IO and improve Buffer Cache efficiency).

And from a comment in the above article, possibly the fix for “Bug 5970280 MERGE has wrong TM lock modes for foreign key constraints”
https://supporthtml.oracle.com/ep/faces/secure/km/DocumentDisplay.jspx?id=5970280.8

The problem that you described is not related to a deadlock which appears in Oracle Database 11g which does not appear in Oracle Database 10g, as described in this blog article.

This blog is not a question and answer forum, however it is a place where I try to help people understand how to find good answers. I am not familiar with “developer 10g” and Oracle Database 11g now includes four different releases (11.1.0.6, 11.1.0.7, 11.2.0.1, 11.2.0.2), each with potentially different behavior. When asking questions it is a very good idea to be very specific, otherwise you may receive an answer which is useless, thus wasting the time of the person answering the question and your own time.

Ask yourself what might prevent you from making changes to any table. My first thought is that you might have established a read-only connection between “developer 10g” and Oracle Database 11g (one of 11.1.0.6, 11.1.0.7, 11.2.0.1, 11.2.0.2). In such a case, you might try a Google search (http://www.google.com) of the Oracle documentation (assuming that “developer 10g” is an Oracle product). The search keywords might look like this:

oracle developer 10g "read only" connection site:download.oracle.com

My second thought is that there is a limitation applied to the database user account that you are using in “developer 10g”. Maybe that account has SELECT permission on the tables, but lacks the UPDATE permission on the tables. To see how to do that, you would use search keywords like this:

oracle grant update permission site:download.oracle.com

I would also try to verify that the same problem is present when using that same user account with another program, such as SQL*Plus.

Before attempting to ask a question:
* Identify the best place to ask a question – it does little good to ask a question on a site that does not answer specific user supplied questions. If there are multiple forums at the site, make certain that you pick the most appropriate forum for your question.
* Clarify what is “developer 10g”, for example, who makes the product and the exact product name.
* Determine the exact Oracle Database release, for example 11.2.0.2.
* Document exactly what you tried when attempting to resolve the problem.

When asking the question:
* Be polite, and do not mention the word “urgent”.
* Provide the table definition of one of the tables and any triggers on the table.
* Provide the EXACT error message that you received from the “developer 10g” product
* Specify the exact Oracle Database release
* Describe the steps that you performed to investigate the problem.

If the question is an Oracle Database type question, pick a question/answer forum that is appropriate for your question. Some of the better sites include:
http://asktom.oracle.com
http://groups.google.com/group/comp.databases.oracle.server/
http://forums.oracle.com/forums/forum.jspa?forumID=61