Re: Wrong rows estimations with joins of CTEs slows queries by more than factor 500

Hi,

I haven't looked at the patch, but please add the patch to the next
commit fest (2023-09), so that we don't lose track of it.

See https://commitfest.postgresql.org


regards

Tomas

On 8/14/23 13:12, Jian Guo wrote:
> Hi hackers,
> 
> I have written a patch to add stats info for Vars in CTEs. With this
> patch, the join size estimation on the upper of CTE scans became more
> accurate.
> 
> In the function |selfuncs.c:eqjoinsel| it uses the number of the
> distinct values of the two join variables to estimate join size, and in
> the function |selfuncs.c:get_variable_numdistinct| return a default
> value |DEFAULT_NUM_DISTINCT| (200 in Postgres and 1000 in Greenplum),
> with the default value, you can never expect a good plan.
> 
> Thanks if anyone could give a review.
> 
> Regards,
> Jian
> 
> ------------------------------------------------------------------------
> *From:* Hans Buschmann <buschmann@nidsa.net>
> *Sent:* Wednesday, February 8, 2023 21:55
> *To:* pgsql-hackers@lists.postgresql.org
> <pgsql-hackers@lists.postgresql.org>
> *Subject:* Wrong rows estimations with joins of CTEs slows queries by
> more than factor 500
>  
>     
> !! External Email
> 
> During data refactoring of our Application I encountered $subject when
> joining 4 CTEs with left join or inner join.
> 
> 
> 1. Background
> 
> PG 15.1 on Windows x64 (OS seems no to have no meening here)
> 
> 
> I try to collect data from 4 (analyzed) tables (up,li,in,ou) by grouping
> certain data (4 CTEs qup,qli,qin,qou)
> 
> The grouping of the data in the CTEs gives estimated row counts of about
> 1000 (1 tenth of the real value) This is OK for estimation.
> 
> 
> These 4 CTEs are then used to combine the data by joining them.
> 
> 
> 2. Problem
> 
> The 4 CTEs are joined by left joins as shown below:
> 
> 
> from qup
> left join qli on (qli.curr_season=qup.curr_season and
> qli.curr_code=qup.curr_code and qli.ibitmask>0 and
> cardinality(qli.mat_arr) <=8)
> left join qin on (qin.curr_season=qup.curr_season and
> qin.curr_code=qup.curr_code and qin.ibitmask>0 and
> cardinality(qin.mat_arr) <=8)
> left join qou on (qou.curr_season=qup.curr_season and
> qou.curr_code=qup.curr_code and qou.ibitmask>0 and
> cardinality(qou.mat_arr) <=11)
> where qup.ibitmask>0 and cardinality(qup.mat_arr) <=21
> 
> The plan first retrieves qup and qli, taking the estimated row counts of
> 1163 and 1147 respectively
> 
> 
> BUT the result is then hashed and the row count is estimated as 33!
> 
> 
> In a Left join the row count stays always the same as the one of left
> table (here qup with 1163 rows)
> 
> 
> The same algorithm which reduces the row estimation from 1163 to 33 is
> used in the next step to give an estimation of 1 row.
> 
> This is totally wrong.
> 
> 
> Here is the execution plan of the query:
> 
> (search the plan for rows=33)
> 
> 
>                                                                    
> QUERY PLAN
>
--------------------------------------------------------------------------------------------------------------------------------------------------
>  Append  (cost=13673.81..17463.30 rows=5734 width=104) (actual
> time=168.307..222.670 rows=9963 loops=1)
>    CTE qup
>      ->  GroupAggregate  (cost=5231.22..6303.78 rows=10320 width=80)
> (actual time=35.466..68.131 rows=10735 loops=1)
>            Group Key: sa_upper.sup_season, sa_upper.sup_sa_code
>            ->  Sort  (cost=5231.22..5358.64 rows=50969 width=18) (actual
> time=35.454..36.819 rows=50969 loops=1)
>                  Sort Key: sa_upper.sup_season, sa_upper.sup_sa_code
> COLLATE "C"
>                  Sort Method: quicksort  Memory: 4722kB
>                  ->  Hash Left Join  (cost=41.71..1246.13 rows=50969
> width=18) (actual time=0.148..10.687 rows=50969 loops=1)
>                        Hash Cond: ((sa_upper.sup_mat_code)::text =
> upper_target.up_mat_code)
>                        ->  Seq Scan on sa_upper  (cost=0.00..884.69
> rows=50969 width=16) (actual time=0.005..1.972 rows=50969 loops=1)
>                        ->  Hash  (cost=35.53..35.53 rows=495 width=6)
> (actual time=0.140..0.140 rows=495 loops=1)
>                              Buckets: 1024  Batches: 1  Memory Usage: 27kB
>                              ->  Seq Scan on upper_target 
> (cost=0.00..35.53 rows=495 width=6) (actual time=0.007..0.103 rows=495
> loops=1)
>                                    Filter: (id_up <= 495)
>                                    Rows Removed by Filter: 1467
>    CTE qli
>      ->  GroupAggregate  (cost=1097.31..1486.56 rows=10469 width=80)
> (actual time=9.446..27.388 rows=10469 loops=1)
>            Group Key: sa_lining.sli_season, sa_lining.sli_sa_code
>            ->  Sort  (cost=1097.31..1126.74 rows=11774 width=18) (actual
> time=9.440..9.811 rows=11774 loops=1)
>                  Sort Key: sa_lining.sli_season, sa_lining.sli_sa_code
> COLLATE "C"
>                  Sort Method: quicksort  Memory: 1120kB
>                  ->  Hash Left Join  (cost=7.34..301.19 rows=11774
> width=18) (actual time=0.045..2.438 rows=11774 loops=1)
>                        Hash Cond: ((sa_lining.sli_mat_code)::text =
> lining_target.li_mat_code)
>                        ->  Seq Scan on sa_lining  (cost=0.00..204.74
> rows=11774 width=16) (actual time=0.008..0.470 rows=11774 loops=1)
>                        ->  Hash  (cost=5.86..5.86 rows=118 width=6)
> (actual time=0.034..0.034 rows=119 loops=1)
>                              Buckets: 1024  Batches: 1  Memory Usage: 13kB
>                              ->  Seq Scan on lining_target 
> (cost=0.00..5.86 rows=118 width=6) (actual time=0.008..0.024 rows=119
> loops=1)
>                                    Filter: (id_li <= 119)
>                                    Rows Removed by Filter: 190
>    CTE qin
>      ->  GroupAggregate  (cost=1427.34..1880.73 rows=10678 width=80)
> (actual time=11.424..31.508 rows=10678 loops=1)
>            Group Key: sa_insole.sin_season, sa_insole.sin_sa_code
>            ->  Sort  (cost=1427.34..1465.41 rows=15230 width=18) (actual
> time=11.416..11.908 rows=15230 loops=1)
>                  Sort Key: sa_insole.sin_season, sa_insole.sin_sa_code
> COLLATE "C"
>                  Sort Method: quicksort  Memory: 1336kB
>                  ->  Hash Left Join  (cost=10.49..369.26 rows=15230
> width=18) (actual time=0.051..3.108 rows=15230 loops=1)
>                        Hash Cond: ((sa_insole.sin_mat_code)::text =
> insole_target.in_mat_code)
>                        ->  Seq Scan on sa_insole  (cost=0.00..264.30
> rows=15230 width=16) (actual time=0.006..0.606 rows=15230 loops=1)
>                        ->  Hash  (cost=9.01..9.01 rows=118 width=6)
> (actual time=0.042..0.043 rows=119 loops=1)
>                              Buckets: 1024  Batches: 1  Memory Usage: 13kB
>                              ->  Seq Scan on insole_target 
> (cost=0.00..9.01 rows=118 width=6) (actual time=0.008..0.032 rows=119
> loops=1)
>                                    Filter: (id_in <= 119)
>                                    Rows Removed by Filter: 362
>    CTE qou
>      ->  GroupAggregate  (cost=2366.22..2986.89 rows=10699 width=80)
> (actual time=18.198..41.812 rows=10699 loops=1)
>            Group Key: sa_outsole.sou_season, sa_outsole.sou_sa_code
>            ->  Sort  (cost=2366.22..2428.14 rows=24768 width=18) (actual
> time=18.187..18.967 rows=24768 loops=1)
>                  Sort Key: sa_outsole.sou_season, sa_outsole.sou_sa_code
> COLLATE "C"
>                  Sort Method: quicksort  Memory: 2317kB
>                  ->  Hash Left Join  (cost=5.39..558.63 rows=24768
> width=18) (actual time=0.046..5.132 rows=24768 loops=1)
>                        Hash Cond: ((sa_outsole.sou_mat_code)::text =
> outsole_target.ou_mat_code)
>                        ->  Seq Scan on sa_outsole  (cost=0.00..430.68
> rows=24768 width=16) (actual time=0.010..1.015 rows=24768 loops=1)
>                        ->  Hash  (cost=5.03..5.03 rows=29 width=6)
> (actual time=0.032..0.032 rows=29 loops=1)
>                              Buckets: 1024  Batches: 1  Memory Usage: 10kB
>                              ->  Seq Scan on outsole_target 
> (cost=0.00..5.03 rows=29 width=6) (actual time=0.010..0.025 rows=29 loops=1)
>                                    Filter: (id_ou <= 29)
>                                    Rows Removed by Filter: 213
>    ->  Hash Join  (cost=1015.85..1319.50 rows=1 width=104) (actual
> time=168.307..215.513 rows=8548 loops=1)
>          Hash Cond: ((qou.curr_season = qli.curr_season) AND
> ((qou.curr_code)::text = (qli.curr_code)::text))
>          Join Filter: ((((qup.ibitmask | qin.ibitmask) | qli.ibitmask) |
> qou.ibitmask) IS NOT NULL)
>          ->  CTE Scan on qou  (cost=0.00..294.22 rows=1189 width=76)
> (actual time=18.200..45.188 rows=10275 loops=1)
>                Filter: ((ibitmask > 0) AND (cardinality(mat_arr) <= 11))
>                Rows Removed by Filter: 424
>          ->  Hash  (cost=1015.83..1015.83 rows=1 width=228) (actual
> time=150.094..150.095 rows=8845 loops=1)
>                Buckets: 16384 (originally 1024)  Batches: 1 (originally
> 1)  Memory Usage: 1899kB
>                ->  Hash Join  (cost=707.35..1015.83 rows=1 width=228)
> (actual time=121.898..147.726 rows=8845 loops=1)
>                      Hash Cond: ((qin.curr_season = qli.curr_season) AND
> ((qin.curr_code)::text = (qli.curr_code)::text))
>                      ->  CTE Scan on qin  (cost=0.00..293.65 rows=1186
> width=76) (actual time=11.425..34.674 rows=10197 loops=1)
>                            Filter: ((ibitmask > 0) AND
> (cardinality(mat_arr) <= 8))
>                            Rows Removed by Filter: 481
>                      ->  Hash  (cost=706.86..706.86 rows=33 width=152)
> (actual time=110.470..110.470 rows=9007 loops=1)
>                            Buckets: 16384 (originally 1024)  Batches: 1
> (originally 1)  Memory Usage: 1473kB
>                            ->  Merge Join  (cost=689.20..706.86 rows=33
> width=152) (actual time=105.862..108.925 rows=9007 loops=1)
>                                  Merge Cond: ((qup.curr_season =
> qli.curr_season) AND ((qup.curr_code)::text = (qli.curr_code)::text))
>                                  ->  Sort  (cost=342.09..344.96
> rows=1147 width=76) (actual time=73.419..73.653 rows=9320 loops=1)
>                                        Sort Key: qup.curr_season,
> qup.curr_code COLLATE "C"
>                                        Sort Method: quicksort  Memory:
> 1391kB
>                                        ->  CTE Scan on qup 
> (cost=0.00..283.80 rows=1147 width=76) (actual time=35.467..71.904
> rows=9320 loops=1)
>                                              Filter: ((ibitmask > 0) AND
> (cardinality(mat_arr) <= 21))
>                                              Rows Removed by Filter: 1415
>                                  ->  Sort  (cost=347.12..350.02
> rows=1163 width=76) (actual time=32.440..32.697 rows=10289 loops=1)
>                                        Sort Key: qli.curr_season,
> qli.curr_code COLLATE "C"
>                                        Sort Method: quicksort  Memory:
> 1349kB
>                                        ->  CTE Scan on qli 
> (cost=0.00..287.90 rows=1163 width=76) (actual time=9.447..30.666
> rows=10289 loops=1)
>                                              Filter: ((ibitmask > 0) AND
> (cardinality(mat_arr) <= 8))
>                                              Rows Removed by Filter: 180
>    ->  Merge Left Join  (cost=2625.49..3399.84 rows=5733 width=104)
> (actual time=4.597..6.700 rows=1415 loops=1)
>          Merge Cond: ((qup_1.curr_season = qou_1.curr_season) AND
> ((qup_1.curr_code)::text = (qou_1.curr_code)::text))
>          ->  Merge Left Join  (cost=1958.66..2135.28 rows=5733
> width=136) (actual time=3.427..3.863 rows=1415 loops=1)
>                Merge Cond: ((qup_1.curr_season = qin_1.curr_season) AND
> ((qup_1.curr_code)::text = (qin_1.curr_code)::text))
>                ->  Merge Left Join  (cost=1293.25..1388.21 rows=5733
> width=104) (actual time=2.321..2.556 rows=1415 loops=1)
>                      Merge Cond: ((qup_1.curr_season =
> qli_1.curr_season) AND ((qup_1.curr_code)::text = (qli_1.curr_code)::text))
>                      ->  Sort  (cost=641.68..656.02 rows=5733 width=72)
> (actual time=1.286..1.324 rows=1415 loops=1)
>                            Sort Key: qup_1.curr_season, qup_1.curr_code
> COLLATE "C"
>                            Sort Method: quicksort  Memory: 204kB
>                            ->  CTE Scan on qup qup_1  (cost=0.00..283.80
> rows=5733 width=72) (actual time=0.009..1.093 rows=1415 loops=1)
>                                  Filter: ((ibitmask < 0) OR
> (cardinality(mat_arr) > 21))
>                                  Rows Removed by Filter: 9320
>                      ->  Sort  (cost=651.57..666.11 rows=5816 width=72)
> (actual time=1.033..1.038 rows=180 loops=1)
>                            Sort Key: qli_1.curr_season, qli_1.curr_code
> COLLATE "C"
>                            Sort Method: quicksort  Memory: 41kB
>                            ->  CTE Scan on qli qli_1  (cost=0.00..287.90
> rows=5816 width=72) (actual time=0.055..1.007 rows=180 loops=1)
>                                  Filter: ((ibitmask < 0) OR
> (cardinality(mat_arr) > 8))
>                                  Rows Removed by Filter: 10289
>                ->  Sort  (cost=665.41..680.24 rows=5932 width=72)
> (actual time=1.104..1.117 rows=481 loops=1)
>                      Sort Key: qin_1.curr_season, qin_1.curr_code
> COLLATE "C"
>                      Sort Method: quicksort  Memory: 68kB
>                      ->  CTE Scan on qin qin_1  (cost=0.00..293.65
> rows=5932 width=72) (actual time=0.016..1.038 rows=481 loops=1)
>                            Filter: ((ibitmask < 0) OR
> (cardinality(mat_arr) > 8))
>                            Rows Removed by Filter: 10197
>          ->  Sort  (cost=666.83..681.69 rows=5944 width=72) (actual
> time=1.163..1.174 rows=417 loops=1)
>                Sort Key: qou_1.curr_season, qou_1.curr_code COLLATE "C"
>                Sort Method: quicksort  Memory: 68kB
>                ->  CTE Scan on qou qou_1  (cost=0.00..294.22 rows=5944
> width=72) (actual time=0.029..1.068 rows=424 loops=1)
>                      Filter: ((ibitmask < 0) OR (cardinality(mat_arr) > 11))
>                      Rows Removed by Filter: 10275
>  Planning Time: 2.297 ms
>  Execution Time: 224.759 ms
> (118 Zeilen)
> 
> 3. Slow query from wrong plan as result on similar case with inner join
> 
> When the 3 left joins above are changed to inner joins like:
> 
> from qup
> join qli on (qli.curr_season=qup.curr_season and
> qli.curr_code=qup.curr_code and qli.ibitmask>0 and
> cardinality(qli.mat_arr) <=8)
> join qin on (qin.curr_season=qup.curr_season and
> qin.curr_code=qup.curr_code and qin.ibitmask>0 and
> cardinality(qin.mat_arr) <=8)
> join qou on (qou.curr_season=qup.curr_season and
> qou.curr_code=qup.curr_code and qou.ibitmask>0 and
> cardinality(qou.mat_arr) <=11)
> where qup.ibitmask>0 and cardinality(qup.mat_arr) <=21
> 
> The same rows estimation takes place as with the left joins, but the
> planner now decides to use a nested loop for the last join, which
> results in a 500fold execution time:
> 
>                                                                  QUERY PLAN
>
--------------------------------------------------------------------------------------------------------------------------------------------
>  Append  (cost=13365.31..17472.18 rows=5734 width=104) (actual
> time=139.037..13403.310 rows=9963 loops=1)
>    CTE qup
>      ->  GroupAggregate  (cost=5231.22..6303.78 rows=10320 width=80)
> (actual time=35.399..67.102 rows=10735 loops=1)
>            Group Key: sa_upper.sup_season, sa_upper.sup_sa_code
>            ->  Sort  (cost=5231.22..5358.64 rows=50969 width=18) (actual
> time=35.382..36.743 rows=50969 loops=1)
>                  Sort Key: sa_upper.sup_season, sa_upper.sup_sa_code
> COLLATE "C"
>                  Sort Method: quicksort  Memory: 4722kB
>                  ->  Hash Left Join  (cost=41.71..1246.13 rows=50969
> width=18) (actual time=0.157..10.715 rows=50969 loops=1)
>                        Hash Cond: ((sa_upper.sup_mat_code)::text =
> upper_target.up_mat_code)
>                        ->  Seq Scan on sa_upper  (cost=0.00..884.69
> rows=50969 width=16) (actual time=0.008..2.001 rows=50969 loops=1)
>                        ->  Hash  (cost=35.53..35.53 rows=495 width=6)
> (actual time=0.146..0.146 rows=495 loops=1)
>                              Buckets: 1024  Batches: 1  Memory Usage: 27kB
>                              ->  Seq Scan on upper_target 
> (cost=0.00..35.53 rows=495 width=6) (actual time=0.006..0.105 rows=495
> loops=1)
>                                    Filter: (id_up <= 495)
>                                    Rows Removed by Filter: 1467
>    CTE qli
>      ->  GroupAggregate  (cost=1097.31..1486.56 rows=10469 width=80)
> (actual time=9.541..27.419 rows=10469 loops=1)
>            Group Key: sa_lining.sli_season, sa_lining.sli_sa_code
>            ->  Sort  (cost=1097.31..1126.74 rows=11774 width=18) (actual
> time=9.534..9.908 rows=11774 loops=1)
>                  Sort Key: sa_lining.sli_season, sa_lining.sli_sa_code
> COLLATE "C"
>                  Sort Method: quicksort  Memory: 1120kB
>                  ->  Hash Left Join  (cost=7.34..301.19 rows=11774
> width=18) (actual time=0.049..2.451 rows=11774 loops=1)
>                        Hash Cond: ((sa_lining.sli_mat_code)::text =
> lining_target.li_mat_code)
>                        ->  Seq Scan on sa_lining  (cost=0.00..204.74
> rows=11774 width=16) (actual time=0.010..0.462 rows=11774 loops=1)
>                        ->  Hash  (cost=5.86..5.86 rows=118 width=6)
> (actual time=0.035..0.035 rows=119 loops=1)
>                              Buckets: 1024  Batches: 1  Memory Usage: 13kB
>                              ->  Seq Scan on lining_target 
> (cost=0.00..5.86 rows=118 width=6) (actual time=0.008..0.025 rows=119
> loops=1)
>                                    Filter: (id_li <= 119)
>                                    Rows Removed by Filter: 190
>    CTE qin
>      ->  GroupAggregate  (cost=1427.34..1880.73 rows=10678 width=80)
> (actual time=11.649..30.910 rows=10678 loops=1)
>            Group Key: sa_insole.sin_season, sa_insole.sin_sa_code
>            ->  Sort  (cost=1427.34..1465.41 rows=15230 width=18) (actual
> time=11.642..12.115 rows=15230 loops=1)
>                  Sort Key: sa_insole.sin_season, sa_insole.sin_sa_code
> COLLATE "C"
>                  Sort Method: quicksort  Memory: 1336kB
>                  ->  Hash Left Join  (cost=10.49..369.26 rows=15230
> width=18) (actual time=0.056..3.144 rows=15230 loops=1)
>                        Hash Cond: ((sa_insole.sin_mat_code)::text =
> insole_target.in_mat_code)
>                        ->  Seq Scan on sa_insole  (cost=0.00..264.30
> rows=15230 width=16) (actual time=0.008..0.594 rows=15230 loops=1)
>                        ->  Hash  (cost=9.01..9.01 rows=118 width=6)
> (actual time=0.045..0.046 rows=119 loops=1)
>                              Buckets: 1024  Batches: 1  Memory Usage: 13kB
>                              ->  Seq Scan on insole_target 
> (cost=0.00..9.01 rows=118 width=6) (actual time=0.008..0.034 rows=119
> loops=1)
>                                    Filter: (id_in <= 119)
>                                    Rows Removed by Filter: 362
>    CTE qou
>      ->  GroupAggregate  (cost=2366.22..2986.89 rows=10699 width=80)
> (actual time=18.163..51.151 rows=10699 loops=1)
>            Group Key: sa_outsole.sou_season, sa_outsole.sou_sa_code
>            ->  Sort  (cost=2366.22..2428.14 rows=24768 width=18) (actual
> time=18.150..20.000 rows=24768 loops=1)
>                  Sort Key: sa_outsole.sou_season, sa_outsole.sou_sa_code
> COLLATE "C"
>                  Sort Method: quicksort  Memory: 2317kB
>                  ->  Hash Left Join  (cost=5.39..558.63 rows=24768
> width=18) (actual time=0.036..5.106 rows=24768 loops=1)
>                        Hash Cond: ((sa_outsole.sou_mat_code)::text =
> outsole_target.ou_mat_code)
>                        ->  Seq Scan on sa_outsole  (cost=0.00..430.68
> rows=24768 width=16) (actual time=0.008..1.005 rows=24768 loops=1)
>                        ->  Hash  (cost=5.03..5.03 rows=29 width=6)
> (actual time=0.024..0.024 rows=29 loops=1)
>                              Buckets: 1024  Batches: 1  Memory Usage: 10kB
>                              ->  Seq Scan on outsole_target 
> (cost=0.00..5.03 rows=29 width=6) (actual time=0.007..0.018 rows=29 loops=1)
>                                    Filter: (id_ou <= 29)
>                                    Rows Removed by Filter: 213
>    ->  Nested Loop  (cost=707.35..1328.37 rows=1 width=104) (actual
> time=139.036..13395.820 rows=8548 loops=1)
>          Join Filter: ((qli.curr_season = qin.curr_season) AND
> ((qli.curr_code)::text = (qin.curr_code)::text))
>          Rows Removed by Join Filter: 88552397
>          ->  Hash Join  (cost=707.35..1016.45 rows=1 width=216) (actual
> time=127.374..168.249 rows=8685 loops=1)
>                Hash Cond: ((qou.curr_season = qli.curr_season) AND
> ((qou.curr_code)::text = (qli.curr_code)::text))
>                ->  CTE Scan on qou  (cost=0.00..294.22 rows=1189
> width=72) (actual time=18.165..54.968 rows=10275 loops=1)
>                      Filter: ((ibitmask > 0) AND (cardinality(mat_arr)
> <= 11))
>                      Rows Removed by Filter: 424
>                ->  Hash  (cost=706.86..706.86 rows=33 width=144) (actual
> time=109.205..109.207 rows=9007 loops=1)
>                      Buckets: 16384 (originally 1024)  Batches: 1
> (originally 1)  Memory Usage: 1369kB
>                      ->  Merge Join  (cost=689.20..706.86 rows=33
> width=144) (actual time=104.785..107.748 rows=9007 loops=1)
>                            Merge Cond: ((qup.curr_season =
> qli.curr_season) AND ((qup.curr_code)::text = (qli.curr_code)::text))
>                            ->  Sort  (cost=342.09..344.96 rows=1147
> width=72) (actual time=72.320..72.559 rows=9320 loops=1)
>                                  Sort Key: qup.curr_season,
> qup.curr_code COLLATE "C"
>                                  Sort Method: quicksort  Memory: 1357kB
>                                  ->  CTE Scan on qup  (cost=0.00..283.80
> rows=1147 width=72) (actual time=35.401..70.834 rows=9320 loops=1)
>                                        Filter: ((ibitmask > 0) AND
> (cardinality(mat_arr) <= 21))
>                                        Rows Removed by Filter: 1415
>                            ->  Sort  (cost=347.12..350.02 rows=1163
> width=72) (actual time=32.461..32.719 rows=10289 loops=1)
>                                  Sort Key: qli.curr_season,
> qli.curr_code COLLATE "C"
>                                  Sort Method: quicksort  Memory: 1269kB
>                                  ->  CTE Scan on qli  (cost=0.00..287.90
> rows=1163 width=72) (actual time=9.543..30.696 rows=10289 loops=1)
>                                        Filter: ((ibitmask > 0) AND
> (cardinality(mat_arr) <= 8))
>                                        Rows Removed by Filter: 180
>          ->  CTE Scan on qin  (cost=0.00..293.65 rows=1186 width=72)
> (actual time=0.001..1.159 rows=10197 loops=8685)
>                Filter: ((ibitmask > 0) AND (cardinality(mat_arr) <= 8))
>                Rows Removed by Filter: 481
>    ->  Merge Left Join  (cost=2625.49..3399.84 rows=5733 width=104)
> (actual time=4.606..6.733 rows=1415 loops=1)
>          Merge Cond: ((qup_1.curr_season = qou_1.curr_season) AND
> ((qup_1.curr_code)::text = (qou_1.curr_code)::text))
>          ->  Merge Left Join  (cost=1958.66..2135.28 rows=5733
> width=136) (actual time=3.479..3.930 rows=1415 loops=1)
>                Merge Cond: ((qup_1.curr_season = qin_1.curr_season) AND
> ((qup_1.curr_code)::text = (qin_1.curr_code)::text))
>                ->  Merge Left Join  (cost=1293.25..1388.21 rows=5733
> width=104) (actual time=2.368..2.610 rows=1415 loops=1)
>                      Merge Cond: ((qup_1.curr_season =
> qli_1.curr_season) AND ((qup_1.curr_code)::text = (qli_1.curr_code)::text))
>                      ->  Sort  (cost=641.68..656.02 rows=5733 width=72)
> (actual time=1.296..1.335 rows=1415 loops=1)
>                            Sort Key: qup_1.curr_season, qup_1.curr_code
> COLLATE "C"
>                            Sort Method: quicksort  Memory: 204kB
>                            ->  CTE Scan on qup qup_1  (cost=0.00..283.80
> rows=5733 width=72) (actual time=0.010..1.119 rows=1415 loops=1)
>                                  Filter: ((ibitmask < 0) OR
> (cardinality(mat_arr) > 21))
>                                  Rows Removed by Filter: 9320
>                      ->  Sort  (cost=651.57..666.11 rows=5816 width=72)
> (actual time=1.069..1.075 rows=180 loops=1)
>                            Sort Key: qli_1.curr_season, qli_1.curr_code
> COLLATE "C"
>                            Sort Method: quicksort  Memory: 41kB
>                            ->  CTE Scan on qli qli_1  (cost=0.00..287.90
> rows=5816 width=72) (actual time=0.057..1.026 rows=180 loops=1)
>                                  Filter: ((ibitmask < 0) OR
> (cardinality(mat_arr) > 8))
>                                  Rows Removed by Filter: 10289
>                ->  Sort  (cost=665.41..680.24 rows=5932 width=72)
> (actual time=1.110..1.124 rows=481 loops=1)
>                      Sort Key: qin_1.curr_season, qin_1.curr_code
> COLLATE "C"
>                      Sort Method: quicksort  Memory: 68kB
>                      ->  CTE Scan on qin qin_1  (cost=0.00..293.65
> rows=5932 width=72) (actual time=0.016..1.046 rows=481 loops=1)
>                            Filter: ((ibitmask < 0) OR
> (cardinality(mat_arr) > 8))
>                            Rows Removed by Filter: 10197
>          ->  Sort  (cost=666.83..681.69 rows=5944 width=72) (actual
> time=1.119..1.128 rows=417 loops=1)
>                Sort Key: qou_1.curr_season, qou_1.curr_code COLLATE "C"
>                Sort Method: quicksort  Memory: 68kB
>                ->  CTE Scan on qou qou_1  (cost=0.00..294.22 rows=5944
> width=72) (actual time=0.029..1.056 rows=424 loops=1)
>                      Filter: ((ibitmask < 0) OR (cardinality(mat_arr) > 11))
>                      Rows Removed by Filter: 10275
>  Planning Time: 1.746 ms
>  Execution Time: 13405.503 ms
> (116 Zeilen)
> 
> This case really brought me to detect the problem!
> 
> The original query and data are not shown here, but the principle should
> be clear from the execution plans.
> 
> I think the planner shouldn't change the row estimations on further
> steps after left joins at all, and be a bit more conservative on inner
> joins.
> This may be related to the fact that this case has 2 join-conditions
> (xx_season an xx_code).
> 
> Thanks for looking
> 
> Hans Buschmann
> 
> 
> 
> 
> 
>     
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> 

-- 
Tomas Vondra
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