Re: Re: sql run time
Date: Mon, 9 Nov 2015 18:18:09 -0600
Message-ID: <CAHSa0M2+hj6NzEnmtABt4kVzZsosACM-wCdAiofxGug=v70U7w_at_mail.gmail.com>
I collected the stats on one of the tables involved friday afternoon and the performance of the query was back to the way it was before. It was almost a shot in the dark, but it seemed to have worked. There are about 5 tables in the query, some have 10 or 20 rows, one has a few thousand, with the biggest having 200K rows. I collected the stats for the 200k row table at 50% and the performance immediately went acceptable. Before that, I tried collecting stats at 10%, 20%, but they did not work. Last week the stats were at about 5% for this table.
I tried comparing the plans, the PHV were the same for both 'good' and the 'bad' plans and the plans looked same to me last week, but look different today - maybe I missed something in the hurry. There were only 20 lines in the plan. The good plan was showing as 0.00 CPU second per exec in the sp report. The bad one was showing up as 0.03 seconds. The SQL was being executed about 200K times per hour.
When it was running unacceptable, I captured some bind values and ran the SQL myself and for all the cases I captured, it returned zero rows; what an irritation when you are executing it several million times a day. As an aside, the db file seq reads are back to 12 ms after the performance got back to the previous level.
Thanks Iggy, Dominic and Lothar and everyone else helped. It will be nice to know why the collection of stats worked.
On Fri, Nov 6, 2015 at 1:48 AM, l.flatz_at_bluewin.ch <l.flatz_at_bluewin.ch> wrote:
> Execution plans can change over time and switch from efficient to
> inefficient. Often an misestimation of cardinality is the cause.
> Quite often such misestmatuion was always there and geting worse with data
> growth. At some point it breaks.
> I rarly deal with past plan though. I want to know what is going wrong NOW
> and how I can stop it.
> On SE, runtime stats would be the measure of choice. Easy and fast to come
> by.
>
> alter session set statistics_level=all;
> run your statement
> select * from table (dbms_xplan.display_cursor(null,null,'RUNSTATS_LAST'));
>
> If strange waits are involved a trace could be helpfull too.
>
> ----Ursprüngliche Nachricht----
> Von : dombrooks_at_hotmail.com
> Datum : 06/11/2015 - 08:14 (GMT)
> An : iggy_fernandez_at_hotmail.com, veeeraman_at_gmail.com,
> oracle-l_at_freelists.org
> Betreff : Re: sql run time
>
>
> It depends (doesn't it always?).
> Potentially if your physical IO time was slower, your SQL could be running
> for longer therefore you might need to do more work to get a read
> consistent picture (more buffer gets) which then makes it even slower, etc
> - circular.
>
>
> On 6 November 2015, at 01:43, Iggy Fernandez <iggy_fernandez_at_hotmail.com>
> wrote:
>
> I don't see how changes in db file sequential read time can impact buffer
> gets
>
> Here are some ways buffer gets can change
>
>
> - Changes in execution plan
> - Changes in data
> - Changes in bind variables (in other words, there is skew in resource
> consumption depending on the bind variables)
> - Effects of the Oracle consistency schema, block cleanout, etc.
>
>
> If you don't have AWR, hopefully you are using Statspack. The sprepsql
> script will give you insight into the execution history.
>
> Iggy
>
>
> ------------------------------
> Date: Thu, 5 Nov 2015 19:30:57 -0600
> Subject: sql run time
> From: veeeraman_at_gmail.com
> To: oracle-l_at_freelists.org
>
> Hi,
>
> We have a 11.2 SE db that is experiencing big spikes in CPU. Upon further
> investigation I see one SQL that has become resource intensive in terms of
> buffer gets and CPU time. The SQL was running fine till few days ago even
> though it was being executed several tens of 1000s of times in the half hr
> reporting period. Per the old reports, this sql has been executed that many
> times always. But something changed few days ago that this SQL shot up in
> terms of # of buffer gets per the report. I tried checking the v$sql for
> different versions today, but I see only one version of the SQL (remembered
> that from Jonathan's advise last time). Is there a way with SE to see the
> equivalent of awrddrpt?
>
> also, I see the dbfile seq read double in value suddenly in the newer
> reports to about 26ms. Even though that is not a great number, the previous
> average was about 12/13ms. I am thinking the increase in the DBF SEQ RD
> time could not cause the increased buffer gets. Am I right in my assumption.
>
> Thanks,
> Ram
>
> --
>
>
>
>
>
-- -- http://www.freelists.org/webpage/oracle-lReceived on Tue Nov 10 2015 - 01:18:09 CET