Oracle SQL indexed query 100% cpu usage - sql

Question

I'm running a relatively simple query
SELECT * FROM confirm_v c
JOIN person p ON c.created_by=p.id
INNER JOIN invoice_confirm ic ON ic.confirm_id=c.id
WHERE c.id = (SELECT id FROM
(SELECT c2.id FROM confirm c2
JOIN invoice_confirm ic2 ON ic2.confirm_id=c2.id
WHERE ic2.invoice_id=11954081
AND c2.previous=0
AND c2.canceled=0
AND c2.confirm_type='INVOICE'
ORDER BY c2.id)
WHERE rownum=1);
which results in 100% cpu usage by the rdb. The confirm_type is a varchar2(50 char), the rest are number(10) if it means anything.
The invoice_confirm and confirm tables are covered by indices and there are no full table scans visible in the execution plan for this query.
This query isn't executed a lot, but accounts for nearly 100% of total cpu usage. Any ideas are appreciated.
EDIT:
The explain plan in text from for the query.
EXPLAIN PLAN FOR ...
SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY());
Plan hash value: 1705859247
------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 69 | 10 (0)| 00:00:01 |
| 1 | NESTED LOOPS | | 1 | 69 | 10 (0)| 00:00:01 |
| 2 | NESTED LOOPS | | 1 | 69 | 10 (0)| 00:00:01 |
| 3 | NESTED LOOPS | | 1 | 57 | 7 (0)| 00:00:01 |
| 4 | NESTED LOOPS | | 1 | 30 | 5 (0)| 00:00:01 |
| 5 | TABLE ACCESS BY INDEX ROWID | CONFIRM | 1 | 24 | 3 (0)| 00:00:01 |
|* 6 | INDEX UNIQUE SCAN | PK_CONFIRM | 1 | | 2 (0)| 00:00:01 |
|* 7 | COUNT STOPKEY | | | | | |
| 8 | VIEW | | 4 | 52 | 27 (4)| 00:00:01 |
|* 9 | SORT ORDER BY STOPKEY | | 4 | 132 | 27 (4)| 00:00:01 |
| 10 | NESTED LOOPS | | 4 | 132 | 26 (0)| 00:00:01 |
| 11 | NESTED LOOPS | | 11 | 132 | 26 (0)| 00:00:01 |
| 12 | TABLE ACCESS BY INDEX ROWID BATCHED| INVOICE_CONFIRM | 3 | 36 | 4 (0)| 00:00:01 |
|* 13 | INDEX RANGE SCAN | FKI_INVOICE_CONFIRM_INVOICE | 2 | | 3 (0)| 00:00:01 |
|* 14 | INDEX UNIQUE SCAN | PK_CONFIRM | 1 | | 1 (0)| 00:00:01 |
|* 15 | TABLE ACCESS BY INDEX ROWID | CONFIRM | 1 | 21 | 2 (0)| 00:00:01 |
|* 16 | INDEX RANGE SCAN | FKI_INVOICE_CONFIRM_CONFIRM | 1 | 6 | 2 (0)| 00:00:01 |
| 17 | TABLE ACCESS BY INDEX ROWID | PERSON | 1 | 27 | 2 (0)| 00:00:01 |
|* 18 | INDEX UNIQUE SCAN | PK_KASUTAJA | 1 | | 1 (0)| 00:00:01 |
|* 19 | INDEX RANGE SCAN | FKI_INVOICE_CONFIRM_CONFIRM | 1 | | 2 (0)| 00:00:01 |
| 20 | TABLE ACCESS BY INDEX ROWID | INVOICE_CONFIRM | 1 | 12 | 3 (0)| 00:00:01 |
------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
6 - access("CONFIRM"."ID"= (SELECT "ID" FROM (SELECT "C2"."ID" "ID" FROM "INVOICE_CONFIRM" "IC2","CONFIRM" "C2"
WHERE "IC2"."CONFIRM_ID"="C2"."ID" AND "C2"."CANCELED"=0 AND "C2"."PREVIOUS"=0 AND "C2"."CONFIRM_TYPE"='INVOICE' AND
"IC2"."INVOICE_ID"=11954081 ORDER BY "C2"."ID") "from$_subquery$_006" WHERE ROWNUM=1))
7 - filter(ROWNUM=1)
9 - filter(ROWNUM=1)
13 - access("IC2"."INVOICE_ID"=11954081)
14 - access("IC2"."CONFIRM_ID"="C2"."ID")
15 - filter("C2"."CANCELED"=0 AND "C2"."PREVIOUS"=0 AND "C2"."CONFIRM_TYPE"='INVOICE')
16 - access("IC"."CONFIRM_ID"="CONFIRM"."ID")
18 - access("CONFIRM"."CREATED_BY"="P"."ID")
19 - access("IC"."CONFIRM_ID"="CONFIRM"."ID")
Note
-----
- dynamic statistics used: dynamic sampling (level=2)
- 2 Sql Plan Directives used for this statement

Answer 1

Gather optimizer statistics on the relevant tables and investigate why the statistics were missing.
begin
dbms_stats.gather_table_stats(user, 'CONFIRM');
dbms_stats.gather_table_stats(user, 'INVOICE_CONFIRM');
dbms_stats.gather_table_stats(user, 'PERSON');
end;
/
Optimizer statistics are critical for Oracle to achieve good performance. The note dynamic statistics used: dynamic sampling (level=2) implies that there are tables with missing optimizer statistics. That should never happen unless the tables were created within the last day.
Oracle automatically gathers stale and missing statistics. Check if the job is running with this query. If there are no recent rows, ask your DBA to re-enable the task.
select *
from dba_optstat_operations
where operation like '%auto%'
order by start_time desc;
The autotask is good enough for most tables. But if there's a large batch process that updates a lot of rows then the statistics should be manually collected as soon as the job is complete.