I've just re-run the test from the blog note.
The problem seems to have gone by 23.3, but it is still present in 19.11
Regards
Jonathan Lewis
On Fri, 3 Nov 2023 at 13:46, Amit Saroha <eramitsaroha@xxxxxxxxx> wrote:
Hello All,
I appreciate your input.
After looking at the statistics, it appears that something is wrong with
them. For example, the PO_RELEASE_ID is inaccurate in a number of the
columns. Additionally, as this is the standard Oracle EBS code for PO line
cancellation, we are unable to alter it.
I'll gather the stats and try again, but I'd appreciate it if you could
look at the attached file and offer some suggestions if stats have to be
gathered in any specific way. Since it is their standard code, I might also
need to open an Oracle SR. However, this could take some time, and the user
would continue to suffer, so any workaround solution would be very
appreciated.
Best Regards,
AMIT
On Fri, Nov 3, 2023 at 8:42 AM Jonathan Lewis <jlewisoracle@xxxxxxxxx>
wrote:
You're right. And that's why it didn't switch. (Though that's not a
good enough reason to change the global setting just for this query, of
course.)
I scanned the list three times and still managed to miss it. Now, if it
had been an underscore !!
Regards
Jonathan Lewis
On Fri, 3 Nov 2023 at 11:49, Timur Akhmadeev <timur.akhmadeev@xxxxxxxxx>
wrote:
There's optimizer_adaptive_reporting_only=true which explains lack of
adaptive execution. It's not a recommended eBS setting BTW.
On Fri, Nov 3, 2023 at 2:38 PM Jonathan Lewis <jlewisoracle@xxxxxxxxx>
wrote:
I didn't say "swap the stats" I said "swap some details of the stats".
It's a fine distinction, but I certainly wouldn't expect Amit to ask for
and import a full metadata export with stats of Jo's table.
Don't forget that the plan is set by the optimizer's best guess of
what's going to happen at run time, so it's fairly irrelevant that one of
the components of the guesswork didn't execute at all. However, it feels a
little suprising that adaptive execution didn't come into play to switch
the hash join to a nested loop join (it is 19c, after all) when the
vw_nso_1 completed and acquired so little data. (I can't see any place in
the output where we could find out if adaptive execution had been disabled
- I thought it would show in the optimizer environment, but there's no
mention there. Maybe there's a restriction on adaptive execution when
there are "conditional" subqueries in play.)
Regards
Jonathan Lewis
On Fri, 3 Nov 2023 at 11:13, Timur Akhmadeev <timur.akhmadeev@xxxxxxxxx>
wrote:
I think swapping stats is not a good idea since the data is different
- things like ORG_ID at least - which will impact estimates with different
inputs in different DB. Changing num_distinct/num_rows/similar things
might
be OK.
It's best to gather stats on the table and indexes and see if the plan
changes - perhaps the index/table stats are not in sync and causing this
bug.
Also I find it funny that lines 15-17 are not even executed because of
the conditional FILTER operation, yet causing misestimates and wrong
choice
of the join method.
On Fri, Nov 3, 2023 at 1:02 PM Jonathan Lewis <jlewisoracle@xxxxxxxxx>
wrote:
There are times when I get to feel really smug!
Maybe you could swap some details of the stats on that table, its
indexes and the column in the critical predicates with Amit to help
identify why the silly cardinality estimate has appeared.
Regards (and thanks)
Jonathan Lewis
On Fri, 3 Nov 2023 at 08:23, Holvoet Jo <J.Holvoet@xxxxxx> wrote:
I can find that exact same sql_id in our Oracle EBS db as well, and
our execution plan is basically doing what Jonathan says : a NL join
between VW_NSO_1 and a unique index scan on PO_LINE_LOCATIONS_U1
instead of
your hash join with a full table scan. We end up with a cost of 6 for
the
update and execution times in the centisecond range (although here it is
hardly ever executed – at most once every few days).
Regards
Jo
--
Regards
Timur Akhmadeev
--
Regards
Timur Akhmadeev
