Re: shared pool waits

Why are the exact stats so important? Do you have queries that need to do different plans between each statistics gathering? You might want to benchmark what happens when you don’t gather statistics so much or at least when you opt for the new automatic delayed invalidation.

It is not a hard parse, but it is a parse.

Cursors will be invalidated as their dependent objects have their stats gathered. I don’t recall how Oracle commits statistics with multiple partitions but it is completely possible for each partition to have new statistics independently, and if your statement doesn’t specify the petition it’s using (using the extended partition syntax) it will be invalidated.

Thanks,
Andy

On Thu, 23 Sep 2021 at 12:22, Pap <oracle.developer35_at_gmail.com> wrote:

> Yes so the underlying table is partitioned table and the stats getting
> gathered on this table during the issue period. And we do have
> no_invalidate set as false in table level ,as we want for some queries to
> use the exact stats information to be used by the
> optimizer immediately after the gathering. And as the table is hash
> partitioned so when it's gathered all the partitions(even its incremental)
> were being gathered and it takes a bit of time for that.
>
> But in that case ,if hard parsing is the only issue, why are we not
> seeing IN_HARD_PARSE column as 'Y' for the most number of sample counts for
> this sql. Also if you see the time model statistics section which i
> shared here , its showing hard parse elapsed time as .6% of the DB time. So
> can it/hard parse be really the issue? But even then, what should we do to
> handle this issue in such a situation?
>
> Another question I was having was , isn't it true that the stats will be
> shared or say the dependent child cursor will be invalidated only after the
> final global stats rollup happens rather with individual gathering on each
> partition?
>
> On Thu, Sep 23, 2021 at 4:07 PM Andy Sayer <andysayer_at_gmail.com> wrote:
>
>> Rolling invalidate sounds like you’re gathering statistics on the
>> dependent tables with rolling cursor invalidation. The default behaviour is
>> that it happens within 5 hours (with some randomness so that you don’t
>> reparse everything at once). See
>>
>> https://blog.toadworld.com/why-my-execution-plan-has-not-been-shared-part-ii
>>
>>
>> It’s an issue if your parse waits are significant enough to be an issue.
>>
>> What is the stats gathering plan for the tables in this query? Anything
>> fun like partitioning?
>>
>> Thanks,
>> Andy
>>
>> On Thu, 23 Sep 2021 at 11:30, Pap <oracle.developer35_at_gmail.com> wrote:
>>
>>> Thank you Andy. If I check now, I am seeing ~11 entries/child cursors in
>>> gv$sql_shared_cusor and all of those ~10 of those having
>>> rolling_invalid_mismatch column as 'Y' and same 10 are also having
>>> 'purged_cursor' column as 'Y'. So is it an issue? Or maybe we have to see
>>> what it looks like when the issue appears i.e. when ~84 child cursors are
>>> created.
>>>
>>> On Thu, Sep 23, 2021 at 3:31 PM Andy Sayer <andysayer_at_gmail.com> wrote:
>>>
>>>> 84 children is quite a lot. Have you checked what the parse reasons
>>>> were in v$sql_shared_cursor ? Worth googling the reasons with inurl:
>>>> https://hourim.wordpress.com/
>>>>
>>>> Hope that helps,
>>>> Andy
>>>>
>>>> On Thu, 23 Sep 2021 at 10:31, Pap <oracle.developer35_at_gmail.com> wrote:
>>>>
>>>>> In our case , optimizer_adaptive_plans TRUE and
>>>>> optimizer_adaptive_statistics as FALSE. But in any case, if this is doing
>>>>> high number of soft parses and that is causing issue, wont this resulted
>>>>> into high number of child cursor or version count. The max number of
>>>>> version count for this sql i saw is ~84 during this ~15 minutes period for
>>>>> ~190K execution of this select query. But yes there is no change in plan
>>>>> its keep using same plan for all the executions. Is this really pointing to
>>>>> an issue related to adaptive feature or parsing?
>>>>>
>>>>> On Thu, Sep 23, 2021 at 3:12 AM Mladen Gogala <gogala.mladen_at_gmail.com>
>>>>> wrote:
>>>>>
>>>>>>
>>>>>> On 9/22/21 11:01, Chris Taylor wrote:
>>>>>> > They came back with this - which is interesting because the
>>>>>> > application issues pretty much the same SQL all the time - so why
>>>>>> > would the SQL be invalid/unable to parse? Odd.
>>>>>>
>>>>>>
>>>>>> The answer are adaptive plans. You get cardinality feedback and your
>>>>>> plan "adapts". In English, that means re-executing a soft parse.
>>>>>>
>>>>>> --
>>>>>> Mladen Gogala
>>>>>> Database Consultant
>>>>>> Tel: (347) 321-1217
>>>>>> https://dbwhisperer.wordpress.com
>>>>>>
>>>>>> --
>>>>>> http://www.freelists.org/webpage/oracle-l
>>>>>>
>>>>>>
>>>>>>

--
http://www.freelists.org/webpage/oracle-l