Wait event problem

Question

I have problem with enq: TM – contention wait events.
From ASH report in Top Event P1/P2/P3 I find problematic object – table T1. It has two columns C1 and C2. There are PK and FK constraints on these two columns.Table T1 has one UNIQUE INDEX - index_name(C1, C2).
With this:
SELECT * FROM (
SELECT c.table_name, cc.column_name, cc.position column_position
FROM   user_constraints c, user_cons_columns cc
WHERE  c.constraint_name = cc.constraint_name
AND    c.constraint_type = 'R'
MINUS
SELECT i.table_name, ic.column_name, ic.column_position
FROM   user_indexes i, user_ind_columns ic
WHERE  i.index_name = ic.index_name
+)+
ORDER BY table_name, column_position;
I find unindexed Foreign Key constraints, and show me that no index on C2 column.
Can I create new index on this C2 column: CREATE INDEX index_name_c2 ON T1(C2) because I have index on C1 and C2 columns ?
In ASH report in Top DB Objects I see another indexes and table with enq: TM – contention event. Whey Oracle show me this objects?

Answer 1

Based on what you've written I see nothing that should stop you from creating an index but I would recommend you do so in dev or test before production.
As to why Oracle is showing it to you? Likely because it thinks there is a potential issue there.
Remember always that the best designed database in the world is going to have a top 5 or top 10 list too. The only way to not have events reported is with shutdown abort.