Re: "micro bucket sort" ...
От | Alvaro Herrera |
---|---|
Тема | Re: "micro bucket sort" ... |
Дата | |
Msg-id | 1281540420-sup-1127@alvh.no-ip.org обсуждение исходный текст |
Ответ на | "micro bucket sort" ... (Hans-Jürgen Schönig <postgres@cybertec.at>) |
Ответы |
Re: "micro bucket sort" ...
Re: "micro bucket sort" ... |
Список | pgsql-hackers |
Excerpts from Hans-Jürgen Schönig's message of mié ago 11 08:21:10 -0400 2010: > same with limit ... > > > test=# explain analyze select * from t_test order by x, y limit 20; But if you put the limit in a subquery which is ordered by the known-indexed condition, it is very fast: alvherre=# explain analyze select * from (select * from t_test order by x limit 20) f order by x, y; QUERY PLAN ─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────Sort (cost=1.24..1.29 rows=20 width=8) (actual time=0.252..0.296 rows=20 loops=1) Sort Key: t_test.x, t_test.y Sort Method: quicksort Memory: 26kB -> Limit (cost=0.00..0.61 rows=20 width=8) (actual time=0.051..0.181 rows=20 loops=1) -> Index Scan using idx_aaaaa on t_test (cost=0.00..30408.36 rows=1000000 width=8) (actual time=0.046..0.098rows=20 loops=1)Total runtime: 0.425 ms (6 filas) I guess it boils down to being able to sort a smaller result set. -- Álvaro Herrera <alvherre@commandprompt.com> The PostgreSQL Company - Command Prompt, Inc. PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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