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Community Blog Performance of PostgreSQL Multi-Field Random Combination Searches

Performance of PostgreSQL Multi-Field Random Combination Searches

In this article, we will explore how to optimize PostgreSQL multi-field and random combination searches with GIN, Bloom, and multiple B-tree indexes.

By Digoal

In one of my previous articles, we looked at the concepts of PostgreSQL optimization using indexes. For PostgreSQL multi-field and random combination searches, there are three optimization techniques:

  1. GIN indexes (supports queries of any field combinations)
  2. Bloom indexes (supports equivalent queries of any read-only combinations)
  3. Every single-column B-tree index (supports queries of any field combinations)

Example

create table test(c1 int, c2 int, c3 int, c4 int, c5 int);

Methods for Creating Bloom, GIN, and Multiple B-Tree Indexes

1. Bloom

postgres=# create extension bloom ;  
CREATE EXTENSION  
postgres=# create index idx_test12_1 on test12 using bloom (c1,c2,c3,c4,c5);  
CREATE INDEX  
postgres=# explain select * from test12 where c1=1;  
                                 QUERY PLAN                                   
----------------------------------------------------------------------------  
 Bitmap Heap Scan on test12  (cost=13.95..20.32 rows=8 width=20)  
   Recheck Cond: (c1 = 1)  
   ->  Bitmap Index Scan on idx_test12_1  (cost=0.00..13.95 rows=8 width=0)  
         Index Cond: (c1 = 1)  
(4 rows)  
postgres=# explain select * from test12 where c1=1 and c2=1;  
                                 QUERY PLAN                                   
----------------------------------------------------------------------------  
 Bitmap Heap Scan on test12  (cost=18.20..19.42 rows=1 width=20)  
   Recheck Cond: ((c1 = 1) AND (c2 = 1))  
   ->  Bitmap Index Scan on idx_test12_1  (cost=0.00..18.20 rows=1 width=0)  
         Index Cond: ((c1 = 1) AND (c2 = 1))  
(4 rows)  
postgres=# explain select * from test12 where c1=1 or c2=1;  
                                    QUERY PLAN                                      
----------------------------------------------------------------------------------  
 Bitmap Heap Scan on test12  (cost=27.91..38.16 rows=17 width=20)  
   Recheck Cond: ((c1 = 1) OR (c2 = 1))  
   ->  BitmapOr  (cost=27.91..27.91 rows=17 width=0)  
         ->  Bitmap Index Scan on idx_test12_1  (cost=0.00..13.95 rows=8 width=0)  
               Index Cond: (c1 = 1)  
         ->  Bitmap Index Scan on idx_test12_1  (cost=0.00..13.95 rows=8 width=0)  
               Index Cond: (c2 = 1)  
(7 rows)

2. Gin

postgres=# create extension btree_gin;  
CREATE EXTENSION  
postgres=# create index idx_test12_1 on test12 using gin (c1,c2,c3,c4,c5);  
CREATE INDEX  
postgres=# explain select * from test12 where c1=1 or c2=1;  
                                   QUERY PLAN                                      
---------------------------------------------------------------------------------  
 Bitmap Heap Scan on test12  (cost=4.94..15.19 rows=17 width=20)  
   Recheck Cond: ((c1 = 1) OR (c2 = 1))  
   ->  BitmapOr  (cost=4.94..4.94 rows=17 width=0)  
         ->  Bitmap Index Scan on idx_test12_1  (cost=0.00..2.46 rows=8 width=0)  
               Index Cond: (c1 = 1)  
         ->  Bitmap Index Scan on idx_test12_1  (cost=0.00..2.46 rows=8 width=0)  
               Index Cond: (c2 = 1)  
(7 rows)  
  
postgres=# explain select * from test12 where c1=1 and c2=1;  
                                QUERY PLAN                                   
---------------------------------------------------------------------------  
 Bitmap Heap Scan on test12  (cost=3.60..4.82 rows=1 width=20)  
   Recheck Cond: ((c1 = 1) AND (c2 = 1))  
   ->  Bitmap Index Scan on idx_test12_1  (cost=0.00..3.60 rows=1 width=0)  
         Index Cond: ((c1 = 1) AND (c2 = 1))  
(4 rows)

3. Multi-btree

postgres=# drop index idx_test12_1 ;  
DROP INDEX  
postgres=# create index idx_test12_1 on test12 using btree(c1);  
CREATE INDEX  
postgres=# create index idx_test12_2 on test12 using btree(c2);  
CREATE INDEX  
postgres=# create index idx_test12_3 on test12 using btree(c3);  
CREATE INDEX  
postgres=# create index idx_test12_4 on test12 using btree(c4);  
CREATE INDEX  
postgres=# create index idx_test12_5 on test12 using btree(c5);  
CREATE INDEX  
  
postgres=# explain select * from test12 where c1=1 and c2=1;  
                                   QUERY PLAN                                      
---------------------------------------------------------------------------------  
 Bitmap Heap Scan on test12  (cost=3.08..4.29 rows=1 width=20)  
   Recheck Cond: ((c2 = 1) AND (c1 = 1))  
   ->  BitmapAnd  (cost=3.08..3.08 rows=1 width=0)  
         ->  Bitmap Index Scan on idx_test12_2  (cost=0.00..1.41 rows=8 width=0)  
               Index Cond: (c2 = 1)  
         ->  Bitmap Index Scan on idx_test12_1  (cost=0.00..1.41 rows=8 width=0)  
               Index Cond: (c1 = 1)  
(7 rows)  
  
postgres=# explain select * from test12 where c1=1 or c2=1;  
                                   QUERY PLAN                                      
---------------------------------------------------------------------------------  
 Bitmap Heap Scan on test12  (cost=2.83..13.09 rows=17 width=20)  
   Recheck Cond: ((c1 = 1) OR (c2 = 1))  
   ->  BitmapOr  (cost=2.83..2.83 rows=17 width=0)  
         ->  Bitmap Index Scan on idx_test12_1  (cost=0.00..1.41 rows=8 width=0)  
               Index Cond: (c1 = 1)  
         ->  Bitmap Index Scan on idx_test12_2  (cost=0.00..1.41 rows=8 width=0)  
               Index Cond: (c2 = 1)  
(7 rows)

What are the performances of GIN, Bloom, and B-Tree bitmap scan?

Wide tables with 1600 columns, search performance of any field combinations

1. Create a table

postgres=# do language plpgsql 
$$
  
declare  
  sql text;  
begin  
  sql := 'create table test1 (';  
  for i in 1..1600 loop  
    sql := sql||' c'||i||' int2 default random()*100,';  
  end loop;  
  sql := rtrim(sql,',');  
  sql := sql||')';  
  execute sql;   
    
  for i in 1..1600 loop   
    execute 'create index idx_test1_'||i||' on test1 (c'||i||')';   
  end loop;  
end;  

$$
;  
DO

2. Write test data

postgres=# insert into test1 (c1)  select generate_series(1,10000);  
INSERT 0 10000

3. Test scripts

vi test.sql  
  
\set c2 random(1,100)  
\set c3 random(1,100)  
\set c4 random(1,100)  
\set c5 random(1,100)  
\set c6 random(1,100)  
\set c7 random(1,100)  
select c1600 from test1 where c2=:c2 and c3=:c3 and c4=:c4 or (c5=:c5 and c6=:c6 and c7=:c7);

4. Testing

pgbench -M prepared -n -r -P 1 -f ./test.sql -c 64 -j 64 -T 120

5. Performance

progress: 33.0 s, 208797.8 tps, lat 0.307 ms stddev 0.016  
progress: 34.0 s, 208516.0 tps, lat 0.307 ms stddev 0.032  
progress: 35.0 s, 208574.0 tps, lat 0.307 ms stddev 0.050  
progress: 36.0 s, 208858.2 tps, lat 0.306 ms stddev 0.013  
progress: 37.0 s, 208686.8 tps, lat 0.307 ms stddev 0.043  
progress: 38.0 s, 208764.2 tps, lat 0.307 ms stddev 0.013

Note: Using prepared statements can reduce hard parsing and improve the performance.

Based on the test, searches of any fields can achieve a response time of 0.3 milliseconds.

PostgreSQL Database ApsaraDB for RDS Multi-Field Search Random Field Search
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