SQL Tuning Advisor (STA) recommends indexes that already exists?

Question

I have enabled the STA to run twice a week, while we are going live with a new application in a new database. I want to insure we have good performance as the load goes up. I was not involved in the original design, which there not not much of, I've discovered. Since we are licensed for it, it seemed like a safe thing to turn on.
The STA ran last night and the report tells me it looked at 736 SQLs with findings, 143 without findings, and skipped 0.
What puzzles me is that, in the "Statistics Finding Summary", it's reporting stale stats on some tables which I know are up to date, as I ran stats on them yesterday and there were no updates to them.
Worse, in the "Index Finding Summary", it reports indexes needed that already do, in fact, exist.
Is there some reason for this? Is there some way to get the STA to be aware of these and avoid the erroneous findings so that I can concentrate on real ones?
Thanks in advance for any suggestions.
PDP

Answer 1

Hi Mark,
Thanks for your interest, yes, the index is being used . Here is the evidence that you were asking about.
It has existed for many weeks, now as the info below will show.
Here is the STA run info, the run was from 2011-07-28 at 11 PM:
========================================
Advisory Type Name Description User Status Start Time Duration (seconds) Expires In (days)
SQL Tuning Advisor SYS_AUTO_SQL_TUNING_TASK Automatic SQL Tuning Task SYS COMPLETED Jul 28, 2011 11:00:03 PM 865 UNLIMITED
Here is part of the Index Finding Summary
=========================================
Index Finding Summary
Table Name Schema References Index Columns
EINSTANCE_ARCH EINTAKE 74 GLOBAL_PATIENT_ID
Drilling into that table, we see the following SQL_ID listed first, "g9uf2kmyvc66y" which is just one of many.
Here is 1 if the sqls, which use the "global_patient_id" as a predicate
(with the many columns that are actually selected not listed as they are not germain:
=====================================================================================
SELECT *
FROM (SELECT '0' AS locked,
(... a whole lot of columns selected)
FROM einstance_arch a
LEFT OUTER JOIN
patient d
ON a.global_patient_id = d.patient_id
LEFT OUTER JOIN
referral e
ON a.instance_id = e.einstance_id,
einstance_states_arch b
WHERE a.current_state = b.inst_state_id
AND a.current_state_id != 15
AND ( a.global_patient_id = 496 )
ORDER BY a.instance_id ASC)
WHERE ROWNUM <= :1
Here's an explain plan extracted from Toad, the index in question is identified by ==>:
======================================================
Plan
SELECT STATEMENT ALL_ROWS Cost: 19 Bytes: 4,528 Cardinality: 4
1 INDEX UNIQUE SCAN INDEX (UNIQUE) EINTAKE.STATES_PK Cost: 0 Bytes: 14 Cardinality: 1
3 SORT AGGREGATE Bytes: 6 Cardinality: 1
2 INDEX RANGE SCAN INDEX EINTAKE.DOCUMENT_ATTR_LNK_INST_ID_IDX2 Cost: 1 Bytes: 6 Cardinality: 1
18 COUNT STOPKEY
17 VIEW EINTAKE. Cost: 19 Bytes: 4,528 Cardinality: 4
16 SORT ORDER BY STOPKEY Cost: 19 Bytes: 1,544 Cardinality: 4
15 NESTED LOOPS
13 NESTED LOOPS Cost: 18 Bytes: 1,544 Cardinality: 4
11 NESTED LOOPS OUTER Cost: 10 Bytes: 1,296 Cardinality: 4
8 HASH JOIN OUTER Cost: 9 Bytes: 1,228 Cardinality: 4
5 TABLE ACCESS BY INDEX ROWID TABLE EINTAKE.EINSTANCE_ARCH Cost: 6 Bytes: 1,152 Cardinality: 4
==> 4 INDEX RANGE SCAN INDEX EINTAKE.EINSTANCE_ARCH_GLBL_PT_ID_IDX3 Cost: 1 Cardinality: 5
7 TABLE ACCESS BY INDEX ROWID TABLE EINTAKE.PATIENT Cost: 2 Bytes: 19 Cardinality: 1
6 INDEX UNIQUE SCAN INDEX (UNIQUE) EINTAKE.PATIENT_PK Cost: 1 Cardinality: 1
10 TABLE ACCESS BY INDEX ROWID TABLE EINTAKE.REFERRAL Cost: 1 Bytes: 17 Cardinality: 1
9 INDEX RANGE SCAN INDEX EINTAKE.REFERRAL_EINSTANCE_ID Cost: 0 Cardinality: 1
12 INDEX UNIQUE SCAN INDEX (UNIQUE) EINTAKE.EINSTANCE_STATES_ARCH_PK Cost: 1 Cardinality: 1
14 TABLE ACCESS BY INDEX ROWID TABLE EINTAKE.EINSTANCE_STATES_ARCH Cost: 2 Bytes: 62 Cardinality: 1
Here is the DDL info on the index in question:
============================
select object_name, created, last_ddl_time from user_objects where object_name = 'EINSTANCE_ARCH_GLBL_PT_ID_IDX3';
OBJECT_NAME CREATED LAST_DDL_TIME
EINSTANCE_ARCH_GLBL_PT_ID_IDX3 2011 07 11 11:22:36 2011 07 11 11:22:36
1 row selected.
Regards,
Paul