Unnesting Subqueries in an Outline
- From: Luke Davies <luke.davies@xxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Thu, 23 Aug 2007 12:15:05 +0100
Hello
We are moving our application from Rule Based Optimisation to Cost Based
Optimisation on 9.2.0.8.0 Standard Edition and have hit a show-stopper
for us. There is one particular query that performs fine (around 10s -
which is acceptable) in RBA but as soon as statistics are gathered then
doesn't come back in under an hour (when we killed it!). The query is
as follows
SELECT f.fund_code
, fp.bid_price
FROM fund_prices fp, funds f
WHERE fp.unp_number = (
SELECT MAX (fp2.unp_number)
FROM fund_prices fp2
WHERE fp2.fund_code = f.fund_code
AND fp2.company_flag = f.company_flag
AND fp2.unit_code = 'B'
AND fp2.mfp_status = 'C')
AND f.fund_code = fp.fund_code
AND f.company_flag = fp.company_flag
AND f.company_flag = 'ISA'
We have got it to work by using a NO_UNNEST hint in the subquery. We
then set the undocumented parameter _unnest_subquery in the parameter
file but this caused everything else to slow down too much.
As it is a bit of a business to get the code changed and we were
therefore wanting to try to use Outlines. However we cannot get them to
work with this query.
We set the OPTIMIZATION_MODE to RULE; created the outline; set the
OPTIMIZATION_MODE back to CHOOSE and then ran the query.
The outline was used - the column USED changed from 'UNUSED' to 'USED'
and V$SQL.OUTLINE_CATEGORY was set to 'DEFAULT' but the query never
returned.
We have logged a call with Oracle who can re-create the problem but we
have had no response other than WIP. The problem does not exist in 10g.
Has anybody got any ideas how we can get this query to perform without
changing the SQL?
Thanks
Luke
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