Re: shared pool waits

Thank you Ahmed. You pointed out this to be an Oracle bug. Can you please shed some more on that regard. What the bug exactly is and the situation when it impacts.

And yes, this database is RAC but this sql is executed from one instance only as per the service configured. We normally see this issue when stats gather on the underlying object which is executing from another instance. Can this be pointing to something else?

On Tue, Sep 21, 2021 at 1:32 PM ahmed.fikri_at_t-online.de < ahmed.fikri_at_t-online.de> wrote:

> You mentioned database 19c. I think the relevant point is whether or not
> you are using RAC. From my observation, this is typical of RAC. The
> problems observed do not occur every day, but when it does happen then jobs
> that were only 2-3 hours in duration take more than 20 hours and removing
> the SQLs that were causing the problem from the shared pool solved the
> problem.
>
>
>
> Best regards
>
> Ahmed
>
>
>
>
>
>
>
>
>
> -----Original-Nachricht-----
>
> Betreff: AW: shared pool waits
>
> Datum: 2021-09-21T09:28:25+0200
>
> Von: "ahmed.fikri_at_t-online.de" <ahmed.fikri_at_t-online.de>
>
> An: "list, oracle" <oracle-l_at_freelists.org>
>
>
>
>
>
>
>
> indeed hard parse in this case is better than waiting eternity due to
> oracle bugs.
>
>
>
>
>
>
>
> -----Original-Nachricht-----
>
> Betreff: Re: shared pool waits
>
> Datum: 2021-09-21T09:11:20+0200
>
> Von: "Pap" <oracle.developer35_at_gmail.com>
>
> An: "ahmed.fikri_at_t-online.de" <ahmed.fikri_at_t-online.de>
>
>
>
>
>
>
> Not getting it fully though. If we purge a sql from cursor cache, doesn't
> it mean there will be hard parsing and that will cause more contention and
> take more CPU to parse subsequently? Though I am also trying to understand
> Lok's point, as we should have noticed the in_hard_parse flag as 'Y' in
> case this issue would have been caused by hard parse.
>
> But again , when I see the P1 and P1text while the ASH shows the event as
> 'library cache:mutex x' or 'cursor mutex s', they are pointing to the same
> sql_text only. Does that mean even doing soft parsing only but because of
> the so many number of executions/soft parses we are suffering? But then I
> am wondering why do we see these issues mainly while stats gathering is
> running from another session on the same underlying object? How can this be
> related?
>
> The query looks like below.
>
>
> SELECT MAX (ID1) FROM TAB1 WHERE C1= :B1 AND C2 = :B2
>
>
> ----------------------------------------------------------------------------------------------------------------
>
> | Id | Operation | Name | Rows | Bytes | Cost
> (%CPU)| Time | Pstart| Pstop |
>
>
> ----------------------------------------------------------------------------------------------------------------
>
> | 0 | SELECT STATEMENT | | | | 4
> (100)| | | |
>
> | 1 | PARTITION RANGE SINGLE | | 1 | 52
> | | | KEY | KEY |
>
> | 2 | SORT AGGREGATE | | 1 | 52
> | | | | |
>
> | 3 | FIRST ROW | | 1 | 52
> | 4 (0)| 00:00:01 | | |
>
> | 4 | INDEX RANGE SCAN (MIN/MAX)| IDX1 | 1 | 52 | 4 (0)|
> 00:00:01 | KEY | KEY |
>
>
> ----------------------------------------------------------------------------------------------------------------
>
>
> On Tue, Sep 21, 2021 at 12:02 PM ahmed.fikri_at_t-online.de <
> ahmed.fikri_at_t-online.de> wrote:
>
>> Hi,
>>
>>
>>
>> pragmatically I used to solve these problems (in my opinion oracle bugs)
>> by creating a scheduler job to detect and remove the SQLs, that cause such
>> problems, from the shared pool (using dbms_shared_pool.purge).
>> Since one can not change the vendor's code.
>>
>>
>>
>> Best regards
>>
>> Ahmed
>>
>>
>>
>>
>>
>>
>>
>> -----Original-Nachricht-----
>>
>> Betreff: shared pool waits
>>
>> Datum: 2021-09-20T21:25:36+0200
>>
>> Von: "Pap" <oracle.developer35_at_gmail.com>
>>
>> An: "Oracle L" <oracle-l_at_freelists.org>
>>
>>
>>
>>
>>
>>
>> Hi , We have a customer application in which we see high wait events like
>> 'cursor:mutex ' and 'library cache lock' for a select query occasionally
>> and thus a specific functionality impacted. This select query(which is part
>> of a plsql procedure) is quick query which runs ~5 million times/hr. But
>> even though number of execution is same mostly throughout the day, it still
>> went through these odd wait events making the per execution time went
>> higher for around ~15 minutes duration causing slowness. And during this
>> period, the ASH shows fro this query, the value of column in_hard_parse as
>> 'N' but in_parse as 'Y' and 'N' both. And we saw we were having stats
>> gather running on that base object during same time. We have no_invalidate
>> set as 'FALSE" as table stats preference, So wanted to understand from
>> experts, can it be really because of 'parsing' issue and we should delete
>> this no_invalidate preference so that it can inherit the default global
>> preference i.e no_invalidate=>auto? The database version is 19C.
>>
> 
>

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