幫助加快MySql查詢

Question

我將如何加快此mysql查詢的速度？

   SET @rank = 0;  

  UPDATE dbTable 
     SET rank_fd = @rank := @rank + 1 
ORDER BY fd2 DESC, fd3 DESC;

該查詢更新了約300,000個表行。 它花費的時間太長。...簡單的控制面板（渦輪面板？）說mysqld僅使用8-9％的cpu。 我知道這永遠都是正確的，但是在我的Core i7機器上查詢的時間幾乎沒有。 我認為在我的P4專用服務器上大約需要5到10分鍾的時間...這不會有問題，除非我必須為不同的值重復執行多次。 它還使其他mysql操作極其緩慢（幾乎掛起），從而極大地影響網站性能。

軟件：

• CentOS版本5.4（最終版），
• 簡單控制面板版本1.4.8，
• PHP 5.2.16
• MySQL客戶端版本：5.1.52

硬件：

• 英特爾奔騰4 CPU 3.0GHz
• 2GB內存

更多信息（於2011年3月6日@ CST下午10:06發布）：

//Core i7 920 @ 2.6GHz, 6GB Ram
UPDATE dbTable SET rank_fd =999999999;
#275037 row(s) affected. ( Query took 7.0708 sec )

SET @rank =0;
#Your SQL query has been executed successfully ( Query took 0.0003 sec )

UPDATE dbTable SET rank_fd = @rank := @rank +1 ORDER BY fd2 DESC, fd3 DESC ;
#275037 row(s) affected. ( Query took 9.9931 sec )



//P4 3.0GHz, 2GB Ram
UPDATE dbTable SET rank_fd =999999999;
#Affected rows: 291468 (Query took 8.2165 sec)

SET @rank =0;
#Your SQL query has been executed successfully (Query took 0.0002 sec)

UPDATE dbTable SET rank_fd = @rank := @rank +1 ORDER BY fd2 DESC, fd3 DESC ;
#Affected rows: 291469 (Query took 305.2104 sec)  

更多信息（於2011年3月7日@ CST下午6:37）：

我有一些新信息。 如果我在P4上執行選擇語句：

SET @rank =0;
SELECT @rank := @rank +1 AS rank_fd FROM dbTable ORDER BY fd2 DESC, fd3 DESC LIMIT 0, 300000;  
#Showing rows 0 - 29 (292,437 total, Query took 3.0448 sec)

計算所有內容僅需3秒。 no-calc批處理更新語句僅需8秒鍾。 根據我的原始陳述，正在做的所有額外工作導致其超過300秒。 在不涉及PHP的select calc語句之后，是否有辦法捕獲更新。 我之所以這樣說，是因為如果我在PHP中循環執行此操作，則它會比原始語句花費更長的時間。

謝謝到目前為止的所有幫助！！！

Answer 1

您正在修改表中的每一行，這當然會很慢。 根據rank_fd的使用方式，您可能只需在fd2和fd3上放置索引並在運行時計算等級就可以fd2 fd3 。

Answer 2

您可以使用存儲過程和臨時表來加快排名過程。

以下示例使用一個擁有150萬行的玩家得分表，並在3個回合（500K * 3）中獲得500K玩家得分，並在大約1輪內更新第1輪（500K行）的排名。 5秒。

希望這可以幫助 ：）

示例表和存儲過程

drop table if exists player_scores;
create table player_scores
(
round_id smallint unsigned not null,
player_id int unsigned not null,
score_1 int unsigned not null default 0,
score_2 int unsigned not null default 0,
rank int unsigned not null default 0,
primary key (round_id, player_id)
)
engine=myisam;

drop procedure if exists update_player_score_ranking;

delimiter #
create procedure update_player_score_ranking
(
p_round_id smallint unsigned
)
begin

  create table tmp_player_scores engine=memory select 
    round_id, player_id, score_1, score_2, @rank:= @rank + 1 as rank
  from 
    player_scores 
  inner join (select @rank:=0) r
  where
   round_id = p_round_id
  order by 
    score_1 desc, score_2 desc;

  delete from player_scores where round_id = p_round_id;
  insert into player_scores select * from tmp_player_scores;

  drop table if exists tmp_player_scores;

end #

delimiter ;

檢測結果：

select count(*) from player_scores;
+----------+
| count(*) |
+----------+
|  1500000 |
+----------+
1 row in set (0.00 sec)

select count(*) from player_scores where round_id = 1;
+----------+
| count(*) |
+----------+
|   500000 |
+----------+
1 row in set (0.07 sec)

select * from player_scores where round_id = 1 order by score_1 desc, score_2 desc limit 5;
+----------+-----------+---------+---------+------+
| round_id | player_id | score_1 | score_2 | rank |
+----------+-----------+---------+---------+------+
|        1 |    456937 |   65534 |   49579 |    0 |
|        1 |     72439 |   65534 |   44537 |    0 |
|        1 |     16427 |   65534 |   43045 |    0 |
|        1 |    259871 |   65534 |   32095 |    0 |
|        1 |    324702 |   65534 |   15227 |    0 |
+----------+-----------+---------+---------+------+
5 rows in set (0.71 sec)


call update_player_score_ranking(1);
Query OK, 0 rows affected (5.57 sec)

select * from player_scores where round_id = 1 order by rank limit 5;
+----------+-----------+---------+---------+------+
| round_id | player_id | score_1 | score_2 | rank |
+----------+-----------+---------+---------+------+
|        1 |    456937 |   65534 |   49579 |    1 |
|        1 |     72439 |   65534 |   44537 |    2 |
|        1 |     16427 |   65534 |   43045 |    3 |
|        1 |    259871 |   65534 |   32095 |    4 |
|        1 |    324702 |   65534 |   15227 |    5 |
+----------+-----------+---------+---------+------+
5 rows in set (1.29 sec)