query with IN expression running slower than query with OR - postgresql

Question

I have two queries one is using OR expression and is running very fast. The other query is similar but is using IN expression instead of OR and is running very slow. I would appreciate if you could let me know how to make the query using IN as fast as the one using OR. The table has 15 million records
SELECT e.id
FROM events e,
resources r
WHERE e.resource_id = r.id
AND resource_type_id IN (19872817,
282)
ORDER BY occurrence_date DESC LIMIT 100
Limit (cost=0.85..228363.80 rows=100 width=12) (actual time=238.668..57470.017 rows=19 loops=1)
-> Nested Loop (cost=0.85..26211499.28 rows=11478 width=12) (actual time=238.667..57470.010 rows=19 loops=1)
Join Filter: (e.resource_id = r.id)
Rows Removed by Join Filter: 507548495
-> Index Scan using eventoccurrencedateindex on events e (cost=0.43..603333.83 rows=15380258 width=16) (actual time=0.023..2798.538 rows=15380258 loops=1)
-> Materialize (cost=0.42..36.16 rows=111 width=4) (actual time=0.000..0.001 rows=33 loops=15380258)
-> Index Scan using resources_type_fk_index on resources r (cost=0.42..35.60 rows=111 width=4) (actual time=0.014..0.107 rows=33 loops=1)
Index Cond: (resource_type_id = ANY ('{19872817,282}'::integer[]))
Total runtime: 57470.057 ms
SELECT e.id
FROM events e,
resources r
WHERE e.resource_id = r.id
AND (resource_type_id = '19872817' OR resource_type_id = '282')
ORDER BY occurrence_date DESC LIMIT 100
Limit (cost=10.17..14.22 rows=100 width=12) (actual time=0.060..0.181 rows=100 loops=1)
-> Nested Loop (cost=10.17..34747856.23 rows=858030913 width=12) (actual time=0.059..0.167 rows=100 loops=1)
Join Filter: (((e.resource_id = r.id) AND (r.resource_type_id = 19872817)) OR (r.resource_type_id = 282))
-> Index Scan using eventoccurrencedateindex on events e (cost=0.43..603333.83 rows=15380258 width=16) (actual time=0.018..0.019 rows=4 loops=1)
-> Materialize (cost=9.74..349.92 rows=111 width=8) (actual time=0.009..0.023 rows=25
loops=4)
-> Bitmap Heap Scan on resources r (cost=9.74..349.36 rows=111 width=8) (actual time=0.034..0.081 rows=33 loops=1)
Recheck Cond: ((resource_type_id = 19872817) OR (resource_type_id = 282))
-> BitmapOr (cost=9.74..9.74 rows=111 width=0) (actual time=0.023..0.023 rows=0 loops=1)
-> Bitmap Index Scan on resources_type_fk_index (cost=0.00..4.84 rows=56 width=0) (actual time=0.009..0.009 rows=0 loops=1)
Index Cond: (resource_type_id = 19872817)
-> Bitmap Index Scan on resources_type_fk_index (cost=0.00..4.84 rows=56 width=0) (actual time=0.014..0.014 rows=33 loops=1)
Index Cond: (resource_type_id = 282)" "Total runtime: 0.242 ms

Answer 1

This is strange in the or version:
Join Filter: (
((e.resource_id = r.id) AND (r.resource_type_id = 19872817))
OR
(r.resource_type_id = 282)
)
It does e.resource_id = r.id AND r.resource_type_id = 19872817 first and then OR r.resource_type_id = 282 which is wrong. Are you sure you issued the correct condition in that query? Notice that there must be parenthesis wrapping the OR:
e.resource_id = r.id
AND
(r.resource_type_id = 19872817 OR r.resource_type_id = 282)