Su una tabella con colonne a, b, c, d, e, f, g, h, i, j, k ottengo:
select * from misty order by a limit 25;
Time: 302.068 ms
E:
select c,b,j,k,a,d,i,g,f,e,h from misty order by a limit 25;
Time: 1258.451 ms
C'è un modo per rendere la selezione per colonna più veloce?
Aggiornare:
Nessun indice su una tabella, uno appena creato
Ecco l'ESPLAIN ANALYZE, non sembra troppo utile:
explain analyze select * from misty order by a limit 25;
Limit (cost=43994.40..43994.46 rows=25 width=190) (actual time=404.958..404.971 rows=25 loops=1)
-> Sort (cost=43994.40..45731.11 rows=694686 width=190) (actual time=404.957..404.963 rows=25 loops=1)
Sort Key: a
Sort Method: top-N heapsort Memory: 28kB
-> Seq Scan on misty (cost=0.00..24390.86 rows=694686 width=190) (actual time=0.013..170.945 rows=694686 loops=1)
Total runtime: 405.019 ms
(6 rows)
E:
explain analyze select c,b,j,k,a,d,i,g,f,e,h from misty order by a limit 25;
Limit (cost=43994.40..43994.46 rows=25 width=190) (actual time=1371.735..1371.745 rows=25 loops=1)
-> Sort (cost=43994.40..45731.11 rows=694686 width=190) (actual time=1371.733..1371.736 rows=25 loops=1)
Sort Key: a
Sort Method: top-N heapsort Memory: 28kB
-> Seq Scan on misty (cost=0.00..24390.86 rows=694686 width=190) (actual time=0.015..516.355 rows=694686 loops=1)
Total runtime: 1371.797 ms
(6 rows)
select *
caso e circa 2,2 secondi per la selezione con colonne elencate in un ordine diverso .
select *
.