RE: Long Parse Time for a big Statement

From: Noveljic Nenad <nenad.noveljic_at_vontobel.com>
Date: Tue, 18 Jan 2022 14:43:00 +0000
Message-ID: <47c33b9d12fc40bc9a2ee83fd283168f_at_vontobel.com>

Jonathan,

Would it make sense to also include die typecheck memory (TCHK) when measuring the total shared memory consumed by an SQL?

For example, in Lothar’s case it was the TCHK allocation that failed.

In some cases, like “create table as select”, the TCHK shared memory can be significantly larger than the SQLA part: https://nenadnoveljic.com/blog/large-tchk-allocations-shared-pool/

Best regards,

Nenad

From: oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> On Behalf Of Jonathan Lewis Sent: Dienstag, 18. Januar 2022 11:56
To: Lothar Flatz <l.flatz_at_bluewin.ch> Cc: Stefan Koehler <contact_at_soocs.de>; oracle-l_at_freelists.org Subject: Re: Long Parse Time for a big Statement

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I've got a note about the memory issue that suggests:

1. explain plan will use SGA memory while parsing information
2. executing the query to get the parsing done will use PGA

In my test case (using 19.11.0.0), executing the query demanded 313MB of PGA; running explain plan for the query used only 47MB At the same time the only significant changes in v$sgastat for explain vs. execute where

shared pool        free memory        470,539,784       Execute
shared pool        free memory        217,137,088       Explain

shared pool        SQLA               40,554,888        Execute
shared pool        SQLA               295,652,112       Explain

In other words: explaining the plan demanded 250MB of memory from the shared pool to use for SQLA

Regards
Jonathan Lewis

On Tue, 18 Jan 2022 at 09:11, Lothar Flatz <l.flatz_at_bluewin.ch<mailto:l.flatz_at_bluewin.ch>> wrote: Hi Stefan,

1.) No, I have not, I would have if I had access to the DB server. I did construct a test case but right now I need to find a server with enough memory to test it.
2.) Yep, there is both. Shared_pool seems to run out first.

   Event waited on                             Times   Max. Wait  Total

Waited

• Waited ----------

  ---

  PGA memory operation 147 0.00 0.00 latch: shared pool 9 0.00 0.00 SGA: allocation forcing component growth 27 2.51 2.51 .. ORA-04031: 80 Byte des Shared Memorys konnten nicht zugewiesen werden ("shared pool","explain plan for SELECT * FR...","TCHK^4b493f9a","logdef: qcopCreateLog")

Thanks

Lothar

Am 18.01.2022 um 10:00 schrieb Stefan Koehler:
> Hello Lothar,
> sorry, if I missed some already explained details in the reply chain.
>
> 1) Have you already sampled the parsing (let's say with 20 CPU samples per second for 2 or 3 minutes or so) and created a flame graph afterwards?
> 2) Are you sure that you are running out of memory in shared pool and not also in PGA? Parsing allocates memory in both areas depending on what is happening.
>
> In the past I almost figured out every long parsing problem with CPU samples and flame graphs (if PARSE timings were not available) - so please have a look at the whole C-stack if you are just concerned about the parsing time but if you are more concerned about the memory usage filter on kghalf, kghalo and kghalp while sampling the C-stacks.
>
> Best Regards
> Stefan Koehler
>
> Independent Oracle performance consultant and researcher
> Website: http://www.soocs.de
> Twitter: _at_OracleSK<
>
>> Lothar Flatz <l.flatz_at_bluewin.ch<mailto:l.flatz_at_bluewin.ch>> hat am 17.01.2022 13:59 geschrieben:
>>
>> Hi,
>>
>> At one customer site we see generated statements, actually reports. The
>> parsetime for such a statement is over an hour, if it finishes at all.
>> It is possible we see "ORA-04031:" when we run out of memory in the
>> shared pool.
>> How big these statements are is hard to tell, since it depends on
>> formatting. With sql developer formatting i get in one typical example >
>> 130000 lines.
>> The statements are constructed relatively simple.
>> It seems to be a kind of change report where columns from different
>> tables are retrieved.
>> At the beginning is a big case statement where a meaningful name is
>> generated for a value followed by this values. I counted 7400 case
>> entries as per statement in one case.
>> I addition we have a number of big inlists.
>> All this is running against a union view of 55 Tables.
>> In other words: If i want to stress the parser I would construct a
>> statement exactly like this.
>> However, one hour seems to be a unrealistically long parse time.
>> Even though that statement needs to be rewritten, but this will take time.
>> I want to know if there is any quick fix like increasing the shared pool
>> a lot. (Which I can't test unfortunately any time soon due lack of memory).
>> Any ideas how to speed up the parse time?
>>
>> Database version is 19.7. Shared Pool size is 20GB
>>
>> Thanks
>>
>> Lothar
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Received on Tue Jan 18 2022 - 15:43:00 CET