The following bug has been logged on the website:
Bug reference: 15948
Logged by: James Inform
Email address: james.inform@pharmapp.de
PostgreSQL version: 11.5
Operating system: Mac OS X 10.13 / Ubuntu 18.04 LTS
Description:
Use the following to reproduce the problem:
create extension pg_trgm;
create table mytable(myid int8 primary key, mytext text);
insert into mytable select g,md5(g::text) from generate_series(1,100000)
g;
create index gin1 on mytable using gin(mytext gin_trgm_ops);
-- Now there is the following record existing in the table
-- myid: 7 mytext: 8f14e45fceea167a5a36dedd4bea2543
-- Now try to query all record which contain "36dedd" AND "4e45f"
-- Using LIKE ALL, a seq scan is used which is very expensive
explain analyze
select * from mytable where mytext like all (array['%36dedd%','%4e45f%']);
-- Seq Scan on mytable (cost=0.00..2185.00 rows=1 width=41) (actual
time=0.012..16.302 rows=1 loops=1)
-- Filter: (mytext ~~ ALL ('{%36dedd%,%4e45f%}'::text[]))
-- Rows Removed by Filter: 99999
-- Planning Time: 0.071 ms
-- Execution Time: 16.312 ms
-- Rewriting the same query with an where clause using the AND operator
works like one would expect from the LIKE ALL
explain analyze
select * from mytable where mytext like '%36dedd%' and mytext like
'%4e45f%';
-- Bitmap Heap Scan on mytable (cost=22.00..23.02 rows=1 width=41) (actual
time=0.136..0.136 rows=1 loops=1)
-- Recheck Cond: ((mytext ~~ '%36dedd%'::text) AND (mytext ~~
'%4e45f%'::text))
-- Heap Blocks: exact=1
-- -> Bitmap Index Scan on gin1 (cost=0.00..22.00 rows=1 width=0)
(actual time=0.130..0.130 rows=1 loops=1)
-- Index Cond: ((mytext ~~ '%36dedd%'::text) AND (mytext ~~
'%4e45f%'::text))
-- Planning Time: 0.084 ms
-- Execution Time: 0.155 ms
So, is this a bug or a feature? ;)
