Re: quick statistics question

From: David Roberts <big.dave.roberts_at_googlemail.com>
Date: Thu, 18 Dec 2014 00:27:24 +0000
Message-ID: <CAOCOAVLOG7vaQrLYnqTJC9c6QzU8wEXAc81_poeqjxCv5qfzOA_at_mail.gmail.com>

We are a year on from a painful 11g upgrade. You don't provide a lot of detail, so my suggestions will be speculative.

I would enquire if you have gathered system statistics. I would also enquire if there are histogram stats on any of the columns on the joins in the poorly performing queries.

System statistics can be quite problematic if not representative. 11g is a lot keener on generating histogram stats than 10g, histogram stats can lead to quite unpredictable performance changes.

The above advice is speculative, if you provide specific oracle version numbers and example plans then we may be able to help you more.

Dave
On 17 Dec 2014 21:29, "Maureen English" <maureen.english_at_alaska.edu> wrote:

> Thanks Mark!
>
> On Wed, Dec 17, 2014 at 10:06 AM, Powell, Mark <mark.powell2_at_hp.com>
> wrote:
>
>> You do not have to delete the statistics before you force the
>> statistics to be re-gathered if you are going to use
>> gather_table_statistics. If will replace what is there.
>>
>>
>>
>>
>>
>> *From:* oracle-l-bounce_at_freelists.org [mailto:
>> oracle-l-bounce_at_freelists.org] *On Behalf Of *Maureen English
>> *Sent:* Wednesday, December 17, 2014 10:25 AM
>> *To:* oracle-l_at_freelists.org
>> *Subject:* quick statistics question
>>
>>
>>
>> We just migrated our reporting instance from 10g to 11g and I planned to
>> let Oracle do all the
>>
>> statistics gathering using the automatic jobs. Unfortunately, I also
>> imported the statistics from
>> the old database as part of the migration and now I have queries that are
>> consistently hanging.
>>
>> I think I need a sanity check. Does it make sense to delete the
>> statistics on the tables
>>
>> involved in these queries, and then gather them with the basic gather
>> table stats statement?
>>
>> Since these are all materialized views that get refreshed (either
>> complete or fast) just about
>> every night, I was hoping that Oracle would just decide that statistics
>> needed to be generated
>> on them after they were refreshed.
>>
>> - Maureen
>>
>
>

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Received on Thu Dec 18 2014 - 01:27:24 CET