Re: Optimizer estimated cardinality very low

Hello, Nenad

Just to clarify, the July partition is the one giving us the very low estimate and does not use the sanity check method.

Having said that, we could test setting a higher value for the column group in the July partition to match what June percentage is and test how that impacts the optimizer. I'll have to look at that process if this is a valid approach.

Thanks,

On Tue, Oct 27, 2020 at 9:05 AM Noveljic Nenad <nenad.noveljic_at_vontobel.com> wrote:

> Hi Daniel,
>
>
>
> *“NUM_DISTINCT for the column_group in July are lower than
> ORDR_RQST_NUMBER instead of being equal or higher.”*
>
>
>
> This is exactly the reason that sanity check kicks in.
>
>
>
>
>
> *“ This happens across other partitions but the estimation doesn't seem
> impacted by this alone.”*
>
>
>
> There is some tolerance range. Set num_distinct for SYS_STU4S$4GK1UDMC2M8$MI#W6QS_
> of the June partition to a sufficiently low value for sanity check to kick
> in. Then you should get sel = 1.0 and a “good” cardinality estimate for
> your case.
>
>
>
>
>
> “*but the estimation doesn't seem impacted by this alone.”*
>
>
>
> Histogram on ORDR_RQST_DATE is apparently another prerequisite for the
> sanity check.
>
>
>
> Best regards,
>
>
>
> Nenad
>
>
>
> https://nenadnoveljic.com/blog
>
>
>
>
>
> *From:* Daniel Coello <coello.daniel_at_gmail.com>
> *Sent:* Montag, 26. Oktober 2020 18:07
> *To:* Noveljic Nenad <nenad.noveljic_at_vontobel.com>
> *Cc:* ORACLE-L (oracle-l_at_freelists.org) <oracle-l_at_freelists.org>
> *Subject:* Re: Optimizer estimated cardinality very low
>
>
>
>
>
> Hi Nenand.
>
>
>
> For when the interval when the estimation is good:
>
> ...
>
> Join ColGroups for ORDER_REQST[ORDER_REQST] and ORDER_DETL[ORDER_DETL] :
> Using cdn sanity check
>
> ...
>
>
>
> Below is some information relevant to the columns:
>
> ORDER_REQST
>
>
>
> PARTITION_NAME
>
> COLUMN_NAME
>
> NUM_DISTINCT
>
> NUM_BUCKETS
>
> SAMPLE_SIZE
>
> HISTOGRAM
>
> NUM_ROW IN PARTITION
>
> JULY
>
> SYS_P971481
>
> ORDR_RQST_DATE
>
> 3
>
> 3
>
> 26895392
>
> FREQUENCY
>
> 26895392
>
> SYS_P971481
>
> SYS_STU4S$4GK1UDMC2M8$MI#W6QS_
>
> 26636288
>
> 1
>
> 26895392
>
> NONE
>
> 26895392
>
> SYS_P971481
>
> ORDR_RQST_NUMBER
>
> 26895392
>
> 1
>
> 26895392
>
> NONE
>
> 26895392
>
> JUNE
>
> SYS_P964661
>
> ORDR_RQST_DATE
>
> 4
>
> 4
>
> 17506471
>
> FREQUENCY
>
> 17506471
>
> SYS_P964661
>
> SYS_STU4S$4GK1UDMC2M8$MI#W6QS_
>
> 15794176
>
> 1
>
> 17506471
>
> NONE
>
> 17506471
>
> SYS_P964661
>
> ORDR_RQST_NUMBER
>
> 15649792
>
> 1
>
> 17506471
>
> NONE
>
> 17506471
>
> ORDER_DETL
>
>
>
> PARTITION_NAME
>
> COLUMN_NAME
>
> NUM_DISTINCT
>
> NUM_BUCKETS
>
> SAMPLE_SIZE
>
> HISTOGRAM
>
> NUM_ROW IN PARTITION
>
> JULY
>
> SYS_P971761
>
> ORDR_RQST_DATE
>
> 3
>
> 3
>
> 32314200
>
> FREQUENCY
>
> 32314200
>
> SYS_P971761
>
> SYS_STU4S$4GK1UDMC2M8$MI#W6QS_
>
> 26636288
>
> 1
>
> 32314200
>
> NONE
>
> 32314200
>
> SYS_P971761
>
> ORDR_RQST_NUMBER
>
> 26984448
>
> 1
>
> 32314200
>
> NONE
>
> 32314200
>
> JUNE
>
> SYS_P964866
>
> ORDR_RQST_DATE
>
> 4
>
> 4
>
> 21814573
>
> FREQUENCY
>
> 21814573
>
> SYS_P964866
>
> SYS_STU4S$4GK1UDMC2M8$MI#W6QS_
>
> 15794176
>
> 1
>
> 21814573
>
> NONE
>
> 21814573
>
> SYS_P964866
>
> ORDR_RQST_NUMBER
>
> 15649792
>
> 1
>
> 21814573
>
> NONE
>
> 21814573
>
>
>
> Things that have been pointed out to me or relevant to the env:
>
> - NUM_DISTINCT for the column_group in July are lower than
> ORDR_RQST_NUMBER instead of being equal or higher. This happens across
> other partitions but the estimation doesn't seem impacted by this alone.
>
> - I added the NUM_ROW values from the partitions for comparison with the
> total number of rows in it.
>
> - ORDER_DETL columns' values should exist in ORDER_REQST, there shouldn't
> be an orphan row which in real counts you can see.
>
>
>
>
>
> - The actual count for distincts are:
>
> *July:*
>
> ORDER_REQST
>
> ORDR_RQST_NUMBER: 26846523
>
> COL_GROUP ( ORDR_RQST_NUMBER , ORDR_RQST_DATE ): 26846523
>
>
>
> ORDER_DETL
>
> ORDR_RQST_NUMBER: 26846523
>
> COL_GROUP ( ORDR_RQST_NUMBER , ORDR_RQST_DATE ) : 26846523
>
>
>
> *June:*
>
> ORDER_REQST
>
> ORDR_RQST_NUMBER : 15683040
>
> COL_GROUP ( ORDR_RQST_NUMBER , ORDR_RQST_DATE ) : 15683040
>
>
>
> ORDER_DETL
>
> ORDR_RQST_NUMBER : 15683040
>
> COL_GROUP ( ORDR_RQST_NUMBER , ORDR_RQST_DATE ) : 15683040
>
>
>
> Thanks,
>
>
>
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-- 
Daniel Coello Villacis

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