Size of IN list affects query plan

Hi,

I would like to know, how does the size of the IN list affect query planner.
I have a query

select distinct on (event_id, tag_id) et.id,
        e.id as event_id, t.id as tag_id, t.name,
        t.user_id, t.shared, t.color,
        case
          when ea.id <> e.id then true
          else false
        end as inherited
from do_event e
      join do_event ea on (ea.tree_id = e.tree_id and ea.lft <= e.lft
and ea.rght >= e.rght)
      join do_event_tags et on (et.event_id = ea.id)
      join do_tag t on (t.id = et.tag_id)
where e.id in (LIST_OF_INTEGERS) and
       (t.user_id = 14 or t.shared)
order by event_id, tag_id, inherited;

and have doubts, if the size of the list does not impact the plan
significantly.

If LIST_OF_INTEGERS has <=233 values, the query is really fast:
  Unique  (cost=2351.85..2353.71 rows=249 width=33) (actual
time=24.515..24.654 rows=163 loops=1)
    ->  Sort  (cost=2351.85..2352.47 rows=249 width=33) (actual
time=24.513..24.549 rows=166 loops=1)
          Sort Key: e.id, t.id, (CASE WHEN (ea.id <> e.id) THEN true
ELSE false END)
          Sort Method: quicksort  Memory: 37kB
          ->  Hash Join  (cost=2217.89..2341.94 rows=249 width=33)
(actual time=18.987..24.329 rows=166 loops=1)
                Hash Cond: (et.event_id = ea.id)
                ->  Hash Join  (cost=4.73..119.62 rows=1612 width=29)
(actual time=0.151..4.634 rows=2312 loops=1)
                      Hash Cond: (et.tag_id = t.id)
                      ->  Seq Scan on do_event_tags et (cost=0.00..79.47
rows=5147 width=12) (actual time=0.006..1.531 rows=5147 loops=1)
                      ->  Hash  (cost=4.08..4.08 rows=52 width=21)
(actual time=0.119..0.119 rows=49 loops=1)
                            Buckets: 1024  Batches: 1  Memory Usage: 3kB
                            ->  Seq Scan on do_tag t (cost=0.00..4.08
rows=52 width=21) (actual time=0.019..0.097 rows=49 loops=1)
                                  Filter: ((user_id = 14) OR shared)
                ->  Hash  (cost=2157.26..2157.26 rows=4472 width=8)
(actual time=18.782..18.782 rows=270 loops=1)
                      Buckets: 1024  Batches: 1  Memory Usage: 11kB
                      ->  Nested Loop  (cost=428.35..2157.26 rows=4472
width=8) (actual time=0.597..18.595 rows=270 loops=1)
                            Join Filter: ((ea.lft <= e.lft) AND (ea.rght
 >= e.rght))
                            ->  Bitmap Heap Scan on do_event e
(cost=428.35..926.22 rows=232 width=16) (actual time=0.568..0.895
rows=233 loops=1)
                                  Recheck Cond: (id = ANY

('{110364,110377,42337,1503,5490,106267,106607,108419,108836,108556,108744,108466,108467,106331,3717,105404,35179,3398,5675,5896,5888,5287,4679,4275,4042,1599,4041,3311,1588,1605,1607,1606,1604,1594,1850,110494,110041,107955,110373,110068,110114,109503,109925,108959,108964,109189,109598,109142,109304,109607,107902,106668,109121,109101,109056,4621,109031,2574,5092,1674,106452,108901,108849,108713,108783,108766,108386,108455,2560,108397,1538,2007,108000,108389,108336,108456,36796,28985,108003,108421,108399,4871,106884,6371,36026,108204,108022,107941,107967,107911,107928,47944,107010,106640,107037,106994,107011,55313,105862,106332,106498,5850,13369,106161,5859,28465,106385,106444,102751,106371,105131,2610,102753,4833,4936,4755,4699,105402,14087,4798,4942,36249,55513,75790,75789,4238,6370,5744,5745,5149,4731,42297,34841,31190,17339,31155,31242,17701,17642,31203,31218,31376,5856,5141,18154,27146,17590,17566,13692,4867,1842,6365,6354,5480,5481,4382,5893,6355,5907,5886,5826,5028,4665,5230,5482,5273,4181,5091,4869,4983,4968,4961,4905,4906,4036,1483,4284,4790,4348,4648,4655,4647,4656,3075,4596,2144,4274,4592,4506,4549,4595,4188,4548,4511,4333,4306,4291,4240,4268,4114,3665,3547,1563,2102,1514,3579,3607,3501,2834,2436,3069,1400,2359,3056,3173,2897,2837,2780,2137,1447,1280,421,412,2076,1200,1691,446,1444,399,374,444,419,449}'::integer[]))
                                  ->  Bitmap Index Scan on
do_event_pkey  (cost=0.00..428.29 rows=232 width=0) (actual
time=0.538..0.538 rows=233 loops=1)
                                        Index Cond: (id = ANY

('{110364,110377,42337,1503,5490,106267,106607,108419,108836,108556,108744,108466,108467,106331,3717,105404,35179,3398,5675,5896,5888,5287,4679,4275,4042,1599,4041,3311,1588,1605,1607,1606,1604,1594,1850,110494,110041,107955,110373,110068,110114,109503,109925,108959,108964,109189,109598,109142,109304,109607,107902,106668,109121,109101,109056,4621,109031,2574,5092,1674,106452,108901,108849,108713,108783,108766,108386,108455,2560,108397,1538,2007,108000,108389,108336,108456,36796,28985,108003,108421,108399,4871,106884,6371,36026,108204,108022,107941,107967,107911,107928,47944,107010,106640,107037,106994,107011,55313,105862,106332,106498,5850,13369,106161,5859,28465,106385,106444,102751,106371,105131,2610,102753,4833,4936,4755,4699,105402,14087,4798,4942,36249,55513,75790,75789,4238,6370,5744,5745,5149,4731,42297,34841,31190,17339,31155,31242,17701,17642,31203,31218,31376,5856,5141,18154,27146,17590,17566,13692,4867,1842,6365,6354,5480,5481,4382,5893,6355,5907,5886,5826,5028,4665,5230,5482,5273,4181,5091,4869,4983,4968,4961,4905,4906,4036,1483,4284,4790,4348,4648,4655,4647,4656,3075,4596,2144,4274,4592,4506,4549,4595,4188,4548,4511,4333,4306,4291,4240,4268,4114,3665,3547,1563,2102,1514,3579,3607,3501,2834,2436,3069,1400,2359,3056,3173,2897,2837,2780,2137,1447,1280,421,412,2076,1200,1691,446,1444,399,374,444,419,449}'::integer[]))
                            ->  Index Scan using do_event_tree_id on
do_event ea  (cost=0.00..5.29 rows=1 width=16) (actual time=0.005..0.040
rows=59 loops=233)
                                  Index Cond: (tree_id = e.tree_id)
  Total runtime: 24.853 ms
(24 rows)

If if has >=234 values, it is very slow:
  Unique  (cost=2379.26..2381.14 rows=250 width=33) (actual
time=3851.030..3851.175 rows=163 loops=1)
    ->  Sort  (cost=2379.26..2379.89 rows=250 width=33) (actual
time=3851.027..3851.073 rows=166 loops=1)
          Sort Key: e.id, t.id, (CASE WHEN (ea.id <> e.id) THEN true
ELSE false END)
          Sort Method: quicksort  Memory: 37kB
          ->  Nested Loop  (cost=139.77..2369.30 rows=250 width=33)
(actual time=44.373..3850.597 rows=166 loops=1)
                Join Filter: ((ea.lft <= e.lft) AND (ea.rght >= e.rght))
                ->  Hash Join  (cost=139.77..1286.83 rows=1612 width=41)
(actual time=10.784..41.107 rows=2312 loops=1)
                      Hash Cond: (ea.id = et.event_id)
                      ->  Seq Scan on do_event ea (cost=0.00..840.97
rows=28997 width=16) (actual time=0.013..10.275 rows=28997 loops=1)
                      ->  Hash  (cost=119.62..119.62 rows=1612 width=29)
(actual time=10.607..10.607 rows=2312 loops=1)
                            Buckets: 1024  Batches: 1  Memory Usage: 137kB
                            ->  Hash Join  (cost=4.73..119.62 rows=1612
width=29) (actual time=0.468..8.024 rows=2312 loops=1)
                                  Hash Cond: (et.tag_id = t.id)
                                  ->  Seq Scan on do_event_tags et
(cost=0.00..79.47 rows=5147 width=12) (actual time=0.007..2.578
rows=5147 loops=1)
                                  ->  Hash  (cost=4.08..4.08 rows=52
width=21) (actual time=0.434..0.434 rows=49 loops=1)
                                        Buckets: 1024  Batches: 1 Memory
Usage: 3kB
                                        ->  Seq Scan on do_tag t
(cost=0.00..4.08 rows=52 width=21) (actual time=0.030..0.405 rows=49
loops=1)
                                              Filter: ((user_id = 14) OR
shared)
                ->  Index Scan using do_event_tree_id on do_event e
(cost=0.00..0.65 rows=1 width=16) (actual time=0.803..1.644 rows=1
loops=2312)
                      Index Cond: (tree_id = ea.tree_id)
                      Filter: (id = ANY

('{110364,110377,42337,1503,5490,106267,106607,108419,108836,108556,108744,108466,108467,106331,3717,105404,35179,3398,5675,5896,5888,5287,4679,4275,4042,1599,4041,3311,1588,1605,1607,1606,1604,1594,1850,110494,110041,107955,110373,110068,110114,109503,109925,108959,108964,109189,109598,109142,109304,109607,107902,106668,109121,109101,109056,4621,109031,2574,5092,1674,106452,108901,108849,108713,108783,108766,108386,108455,2560,108397,1538,2007,108000,108389,108336,108456,36796,28985,108003,108421,108399,4871,106884,6371,36026,108204,108022,107941,107967,107911,107928,47944,107010,106640,107037,106994,107011,55313,105862,106332,106498,5850,13369,106161,5859,28465,106385,106444,102751,106371,105131,2610,102753,4833,4936,4755,4699,105402,14087,4798,4942,36249,55513,75790,75789,4238,6370,5744,5745,5149,4731,42297,34841,31190,17339,31155,31242,17701,17642,31203,31218,31376,5856,5141,18154,27146,17590,17566,13692,4867,1842,6365,6354,5480,5481,4382,5893,6355,5907,5886,5826,5028,4665,5230,5482,5273,4181,5091,4869,4983,4968,4961,4905,4906,4036,1483,4284,4790,4348,4648,4655,4647,4656,3075,4596,2144,4274,4592,4506,4549,4595,4188,4548,4511,4333,4306,4291,4240,4268,4114,3665,3547,1563,2102,1514,3579,3607,3501,2834,2436,3069,1400,2359,3056,3173,2897,2837,2780,2137,1447,1280,421,412,2076,1200,1691,446,1444,399,374,444,419,449,1021}'::integer[]))
  Total runtime: 3851.458 ms
(22 rows)

Increasing effective_cache_size or work_mem does not seem to have impact.


Thanks for any hint,

John