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@xxxxxxxxx>
Sent: Montag, 26. Oktober 2020 18:07
To: Noveljic Nenad <nenad.noveljic@xxxxxxxxxxxx>
Cc: ORACLE-L (oracle-l@xxxxxxxxxxxxx) <oracle-l@xxxxxxxxxxxxx>
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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