Ho questa domanda:
SELECT *
FROM location
WHERE to_tsvector('simple',unaccent2("city"))
@@ to_tsquery('simple',unaccent2('wroclaw'))
order by displaycount
Ne sono contento:
"Sort (cost=3842.56..3847.12 rows=1826 width=123) (actual time=1.915..2.084 rows=1307 loops=1)"
" Sort Key: displaycount"
" Sort Method: quicksort Memory: 206kB"
" -> Bitmap Heap Scan on location (cost=34.40..3743.64 rows=1826 width=123) (actual time=0.788..1.208 rows=1307 loops=1)"
" Recheck Cond: (to_tsvector('simple'::regconfig, unaccent2((city)::text)) @@ '''wroclaw'''::tsquery)"
" -> Bitmap Index Scan on location_lower_idx (cost=0.00..33.95 rows=1826 width=0) (actual time=0.760..0.760 rows=1307 loops=1)"
" Index Cond: (to_tsvector('simple'::regconfig, unaccent2((city)::text)) @@ '''wroclaw'''::tsquery)"
"Total runtime: 2.412 ms"
Ma quando aggiungo LIMIT, l'esecuzione richiede più di 2 secondi:
SELECT *
FROM location
WHERE to_tsvector('simple',unaccent2("city"))
@@ to_tsquery('simple',unaccent2('wroclaw'))
order by displaycount
limit 20
Spiegare:
"Limit (cost=0.00..1167.59 rows=20 width=123) (actual time=2775.452..2775.643 rows=20 loops=1)"
" -> Index Scan using location_displaycount_index on location (cost=0.00..106601.25 rows=1826 width=123) (actual time=2775.448..2775.637 rows=20 loops=1)"
" Filter: (to_tsvector('simple'::regconfig, unaccent2((city)::text)) @@ '''wroclaw'''::tsquery)"
"Total runtime: 2775.693 ms"
Penso che sia un problema con ORDER BY e LIMIT. Come posso forzare PostgreSQL a utilizzare l'indice e fare l'ordine alla fine?
La subquery non aiuta:
SELECT *
FROM (
SELECT *
FROM location
WHERE to_tsvector('simple',unaccent2("city"))
@@ to_tsquery('simple',unaccent2('wroclaw'))
order by displaycount
) t
LIMIT 20;
o:
SELECT *
FROM (
SELECT *
FROM location
WHERE to_tsvector('simple',unaccent2("city"))
@@ to_tsquery('simple',unaccent2('wroclaw'))
) t
order by displaycount
LIMIT 20;