LOWER LIKE vs iLIKE

Question

How does the performance of the following two query components compare?

LOWER LIKE

... LOWER(description) LIKE \'%abcde%\' ...
         


        

Answer 1

In my rails Project. ILIKE is almost 10x faster then LOWER LIKE, I add a GIN index on entities.name column

> Entity.where("LOWER(name) LIKE ?", name.strip.downcase).limit(1).first
Entity Load (2443.9ms)  SELECT  "entities".* FROM "entities" WHERE (lower(name) like 'baidu') ORDER BY "entities"."id" ASC LIMIT $1  [["LIMIT", 1]]

> Entity.where("name ILIKE ?", name.strip).limit(1).first
Entity Load (285.0ms)  SELECT  "entities".* FROM "entities" WHERE (name ilike 'Baidu') ORDER BY "entities"."id" ASC LIMIT $1  [["LIMIT", 1]]

# explain analyze SELECT  "entities".* FROM "entities" WHERE (name ilike 'Baidu') ORDER BY "entities"."id" ASC LIMIT 1;
                                                                   QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=3186.03..3186.04 rows=1 width=1588) (actual time=7.812..7.812 rows=1 loops=1)
   ->  Sort  (cost=3186.03..3187.07 rows=414 width=1588) (actual time=7.811..7.811 rows=1 loops=1)
         Sort Key: id
         Sort Method: quicksort  Memory: 26kB
         ->  Bitmap Heap Scan on entities  (cost=1543.21..3183.96 rows=414 width=1588) (actual time=7.797..7.805 rows=1 loops=1)
               Recheck Cond: ((name)::text ~~* 'Baidu'::text)
               Rows Removed by Index Recheck: 6
               Heap Blocks: exact=7
               ->  Bitmap Index Scan on index_entities_on_name  (cost=0.00..1543.11 rows=414 width=0) (actual time=7.787..7.787 rows=7 loops=1)
                     Index Cond: ((name)::text ~~* 'Baidu'::text)
 Planning Time: 6.375 ms
 Execution Time: 7.874 ms
(12 rows)

GIN index is really helpful to improve ILIKE performance