Hi Steve,
Could you please send us the result for both tests using the display_cursor
select * from table(dbms_xplan.display_cursor('*SQL_ID*',null,'advanced'));
2015-09-23 12:08 GMT+01:00 l.flatz@xxxxxxxxxx <l.flatz@xxxxxxxxxx>:
Hi STeve,
that would be explain plan. Please check out this:
http://kerryosborne.oracle-guy.com/2008/10/explain-plan-lies/
Jonathan is correct of course. The real plan would likely be differnt.
In sqlplus please use dbms_xplan.display_cursor to retrieve the real plan
from the shared pool.
regards
Lothar
----Ursprüngliche Nachricht----
Von : sjb1970@xxxxxxxxx
Datum : 23/09/2015 - 12:54 (UTC)
An : jonathan@xxxxxxxxxxxxxxxxxx
Cc : oracle-l@xxxxxxxxxxxxx
Betreff : Re: query performance following 12c upgrade
Hi Jonathan,
Thanks for the reply.
The plans I've been looking at are from sqplus with autotrace on - is that
incorrect?
Steve
On Wed, Sep 23, 2015 at 11:30 AM, Jonathan Lewis <
jonathan@xxxxxxxxxxxxxxxxxx> wrote:
The difference in performance is so extreme that I'd first have to check
whether or not the plans were true, they look like plans from EXPLAIN PLAN
rather than plans pulled from memory. It would also help to see the
predicate sections anyway.
If these really are the run-time plans with such a massive difference in
performance I'd also want to check for any significant changes in data
content, or physical data location.
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
@jloracle
------------------------------
*From:* oracle-l-bounce@xxxxxxxxxxxxx [oracle-l-bounce@xxxxxxxxxxxxx] on
behalf of Steve Bradshaw [sjb1970@xxxxxxxxx]
*Sent:* 23 September 2015 11:08
*To:* ORACLE-L
*Subject:* query performance following 12c upgrade
Hi,
Looking for ideas as to why a query has started taking a lot longer to
execute since upgrading to 12.1.0.2 from 11.2.0.3.
Its a simple 1 table query, that is performing an index skip scan.
Under 12c, the query is taking 12-13 seconds to return a row, whereas
previously it was a fraction of a second.
There is a difference in the plans between the 2 versions. Under 12c,
the table access is 'TABLE ACCESS BY INDEX ROWID BATCHED'.
From the 12c database:
------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows |
Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2
| 76 | 573 (80)| 00:00:01 |
|* 1 | TABLE ACCESS BY INDEX ROWID BATCHED| TABLE1 | 2
| 76 | 573 (80)| 00:00:01 |
|* 2 | INDEX SKIP SCAN | TABLE1_IDX_7 | 7
| | 572 (80)| 00:00:01 |
------------------------------------------------------------------------------------------------------
From the 12c database (having set optimizer_features_enabled to 11.2.0.3
for the session):
----------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |
Cost (%CPU)| Time |
----------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 38
| 573 (80)| 00:00:01 |
|* 1 | TABLE ACCESS BY INDEX ROWID| TABLE1 | 1 | 38
| 573 (80)| 00:00:01 |
|* 2 | INDEX SKIP SCAN | TABLE1_IDX_7 | 7
| | 572 (80)| 00:00:01 |
----------------------------------------------------------------------------------------------
Any ideas how I can fix this without changing the parameter at the
database level?
Thanks in advance,
Steve
