Re: Sudden plan change related to "VIEW PUSHED PREDICATE" with cost difference of 1M VS 13G

>
> _at_Andy , Regarding the "nested loop outer" while MERGE INTO i.e at the top
> of the plan, If i see the before patch plan which was running fast, in that
> this was NESTED LOOP OUTER only. But yes as you said , i will try to force
> if at all i will be able to make that 'HASH JOIN OUTER' any way.

You need to consider the whole thing. Consider a nested loop index lookup that is working its way through thousands of rows - it could be faster with a hash join full table scan. If you just swap the index lookup to the tablescan then you've made it many times worse. If you swap the nested loops for hash join at the same time you've made it many times better.

The live monitor you shared gave me enough information to know that all hash joins for this part would be a decent idea. But It has only switched the plan halfway, making everything suck.

You can also use explain plan with my suggested (estimated) hints or the rewrite I've shared. Although, there is no substitute for running it against a representative data set on your development environment (but you should get the explain plan first to make sure it's going to do what it looks like we're trying to get it to do). To be clear - my hints are to make it complete the plan change from nested loop indexes to hash joins, my rewrite is to help you get your old plan back with nested loop indexes (and I must note that the indexes being used could do with some improvement if you really want to go down this route).

I don't think you're going to have any luck pursuing a stats problem here - if it was down to statistics, a hint would work (assuming you are using it correctly).

Thanks,
Andrew

On Thu, 12 May 2022 at 19:07, Pap <oracle.developer35_at_gmail.com> wrote:

> I checked dba_tab_col_statistics for HIST table but don't see any column
> group existing so wondering from where it's getting that. Can it be picking
> that from the index stats? If that's the case it's hard to alter that.
>
> On Thu, 12 May 2022, 9:23 pm Noveljic Nenad, <nenad.noveljic_at_vontobel.com>
> wrote:
>
>> This one – HIST, LASTHIST on HIST:
>>
>>
>>
>> ColGroup cardinality sanity check: ndv for HIST[HIST] = 45569134.000000
>> HIST[LASTHIST] = 45569134.000000
>>
>> Join selectivity using 1 ColGroups: 2.1945e-08 (sel1 = 0.000000, sel2 =
>> 0.000000)
>>
>>
>>
>>
>>
>> *From:* oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> *On
>> Behalf Of *Noveljic Nenad
>> *Sent:* Donnerstag, 12. Mai 2022 17:51
>> *To:* Pap <oracle.developer35_at_gmail.com>; Andy Sayer <andysayer_at_gmail.com>;
>> Mohamed Houri <mohamed.houri_at_gmail.com>
>> *Cc:* Oracle L <oracle-l_at_freelists.org>
>> *Subject:* RE: Sudden plan change related to "VIEW PUSHED PREDICATE"
>> with cost difference of 1M VS 13G
>>
>>
>>
>> Can you try to delete (on the test system) the column group statistics
>> that produced a suspiciously low selectivity?
>>
>>
>>
>> JPPD: Retrieved original view card: 45569134.000000
>>
>> Join Card: 0.000000 = outer (0.000000) * inner (45569134.000000) * sel
>> (2.1945e-08)
>>
>> Join Card - Rounded: 1 Computed: 0.000000
>>
>> Best:: JoinMethod: NestedLoop
>>
>> Cost: 39.073380 Degree: 1 Resp: 39.073380 Card: 0.000000 Bytes:
>>
>> ***********************
>>
>> Best so far: Table#: 0 cost: 5.002757 card: 0.000000 bytes: 55.000000
>>
>> Table#: 1 cost: 39.073380 card: 0.000000 bytes:
>> 120.000000
>>
>> ***********************
>>
>> (newjo-stop-1) k:0, spcnt:0, perm:1, maxperm:2000
>>
>> JPPD: Updated best state, Cost = 39.073380
>>
>> JPPD: Will not use JPPD from query block SEL$B29E968D (#5)
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> *From:* Pap <oracle.developer35_at_gmail.com>
>> *Sent:* Donnerstag, 12. Mai 2022 17:41
>> *To:* Noveljic Nenad <nenad.noveljic_at_vontobel.com>; Andy Sayer <
>> andysayer_at_gmail.com>; Mohamed Houri <mohamed.houri_at_gmail.com>
>> *Cc:* Oracle L <oracle-l_at_freelists.org>
>> *Subject:* Re: Sudden plan change related to "VIEW PUSHED PREDICATE"
>> with cost difference of 1M VS 13G
>>
>>
>>
>> **** E-Mail from outside Vontobel:* Do not click on links or open
>> attachments unless you know the content is safe. ***
>>
>> I have captured the snippets from the 10053 trace with JPPD keyword
>> section as pasted in below link. But unable to see any straight forward
>> reason like fix_control or parameter as the cause.
>>
>> https://gist.github.com/oracle9999/95a65f6725e2bb65949d4909652dc59a
>>
>>
>>
>> On Thu, 12 May 2022, 5:00 pm Noveljic Nenad, <nenad.noveljic_at_vontobel.com>
>> wrote:
>>
>> Explain plan won’t execute the query.
>>
>>
>>
>> Look for the lines in the trace containing JPPD.
>>
>>
>>
>> *From:* Pap <oracle.developer35_at_gmail.com>
>> *Sent:* Donnerstag, 12. Mai 2022 13:22
>> *To:* Mohamed Houri <mohamed.houri_at_gmail.com>; Andy Sayer <
>> andysayer_at_gmail.com>; Noveljic Nenad <nenad.noveljic_at_vontobel.com>
>> *Cc:* Oracle L <oracle-l_at_freelists.org>
>> *Subject:* Re: Sudden plan change related to "VIEW PUSHED PREDICATE"
>> with cost difference of 1M VS 13G
>>
>>
>>
>> As we dont really want to run the MERGE/DML query on production. And also
>> the MERGE query is not able to finish with the new path , So is it okay to
>> just do like below explain plan to get the 10053 trace? Hoping that the
>> MERGE query will not be executed behind the scene but just the plan will be
>> generated. Please correct me if wrong here.
>>
>> alter session set tracefile_identifier='mergequeryplan';
>>
>> alter session set events='10053 trace name context forever, level 1';
>>
>> Explain plan for MERGE INTO HIST.....;
>>
>> alter session set events='10053 trace name context off';
>>
>>
>>
>> _at_Mohamed, Regarding the nested loop and hash join which is happening
>> towards the end of the plan, yes both of the sql monitor which i posted for
>> "post patch" are running slow.
>>
>> _at_Andy , Regarding the "nested loop outer" while MERGE INTO i.e at the top
>> of the plan, If i see the before patch plan which was running fast, in that
>> this was NESTED LOOP OUTER only. But yes as you said , i will try to force
>> if at all i will be able to make that 'HASH JOIN OUTER' any way.
>>
>>
>>
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