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  • Какая быстрая база данных для интернет-магазина с более чем 50 тысячами товаров и поиском?

    Vakiliy
    @Vakiliy
    Сделайте вложенный запрос перед использованием unnest,
    Вложенный запрос
    explain (analyze) select unnest(tags) from (SELECT tags FROM t5 WHERE tags @> array['param-1'] group by 1) as t group by 1;
                                                              QUERY PLAN                                                           
    -------------------------------------------------------------------------------------------------------------------------------
     HashAggregate  (cost=14655.30..14660.38 rows=1000 width=84) (actual time=490.721..490.722 rows=10 loops=1)
       ->  Subquery Scan on t  (cost=14647.62..14652.80 rows=1000 width=84) (actual time=490.690..490.706 rows=55 loops=1)
             ->  HashAggregate  (cost=14647.62..14647.73 rows=10 width=84) (actual time=490.676..490.676 rows=10 loops=1)
                   ->  Seq Scan on t5  (cost=0.00..13459.00 rows=475450 width=84) (actual time=0.033..181.649 rows=475324 loops=1)
                         Filter: (tags @> '{param-1}'::text[])
                         Rows Removed by Filter: 24676
     Total runtime: 490.843 ms
    (7 rows)

    Исходный
    explain (analyze) SELECT unnest(tags) FROM t5 WHERE tags @> array['param-1'] group by 1;
                                                          QUERY PLAN                                                       
    -----------------------------------------------------------------------------------------------------------------------
     HashAggregate  (cost=368857.88..368862.95 rows=1000 width=84) (actual time=1196.758..1196.759 rows=10 loops=1)
       ->  Seq Scan on t5  (cost=0.00..249995.38 rows=47545000 width=84) (actual time=0.020..680.547 rows=2501231 loops=1)
             Filter: (tags @> '{param-1}'::text[])
             Rows Removed by Filter: 24676
     Total runtime: 1196.790 ms
    (5 rows)

    Вложенный с seqscan off

    с set enable_seqscan to off;
    explain (analyze) select unnest(tags) from (SELECT tags FROM t5 WHERE tags @> array['param-1'] group by 1) as t group by 1;
                                                                          QUERY PLAN                                                                      
    ------------------------------------------------------------------------------------------------------------------------------------------------------
     HashAggregate  (cost=19433.16..19438.24 rows=1000 width=84) (actual time=411.248..411.249 rows=10 loops=1)
       ->  Subquery Scan on t  (cost=19425.49..19430.66 rows=1000 width=84) (actual time=411.220..411.233 rows=55 loops=1)
             ->  HashAggregate  (cost=19425.49..19425.59 rows=10 width=84) (actual time=411.205..411.206 rows=10 loops=1)
                   ->  Bitmap Heap Scan on t5  (cost=5084.74..18236.86 rows=475450 width=84) (actual time=74.696..126.809 rows=475324 loops=1)
                         Recheck Cond: (tags @> '{param-1}'::text[])
                         ->  Bitmap Index Scan on t5_tagx_gist  (cost=0.00..4965.87 rows=475450 width=0) (actual time=73.514..73.514 rows=475324 loops=1)
                               Index Cond: (tags @> '{param-1}'::text[])
     Total runtime: 411.337 ms
    (8 rows)

    исходные данные:
    create table t5 as (select i id, rand_array() tags from generate_series(1,500000) as i);
    create index t5_tagx_gin on t5 using gin (tags);
    
    create or replace function rand_array() returns text[][] as $$
    begin
     return (select array_agg(t1.col1) from (select format('param-%s', i) col1 from generate_series(1,rand(10)) as i) as t1);
    end;
    $$ language 'plpgsql' strict;


    ЗЫ, i5 2410M 8gb, PostgreSQL 9.3.4 on x86_64-unknown-linux-gnu
    Ответ написан