MySQL簡單選擇查詢很慢

Question

我有大約110.000.000項的大型mysql表

表設計為：

CREATE TABLE IF NOT EXISTS `tracksim` (
`tracksimID` int(11) NOT NULL AUTO_INCREMENT,
`trackID1` int(11) NOT NULL,
`trackID2` int(11) NOT NULL,
`sim` double NOT NULL,
PRIMARY KEY (`tracksimID`),
UNIQUE KEY `TrackID1` (`trackID1`,`trackID2`),
KEY `sim` (`sim`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8;

現在我要查詢一個普通查詢：

SELECT trackID1, trackID2 FROM `tracksim` 
WHERE sim > 0.5 AND 
      (`trackID1` = 168123 OR `trackID2`= 168123)
ORDER BY sim DESC LIMIT 0,100

Explain語句給我：

+----+-------------+----------+-------+---------------+------+---------+------+----------+----------+-------------+
| id | select_type | table    | type  | possible_keys | key  | key_len | ref  | rows     | filtered | Extra       |
+----+-------------+----------+-------+---------------+------+---------+------+----------+----------+-------------+
|  1 | SIMPLE      | tracksim | range | TrackID1,sim  | sim  | 8       | NULL | 19980582 |   100.00 | Using where |
+----+-------------+----------+-------+---------------+------+---------+------+----------+----------+-------------+

該查詢似乎很慢（約185秒），但我不知道是否僅是因為表中的項目數量。 您有提示如何加快查詢速度或查表嗎？

Answer 1

擁有1億1千萬條記錄，我無法想象有很多條目的曲目ID有問題。 我會有諸如

(trackID1, sim )
(trackID2, sim )
(tracksimID, sim)

並通過聯合進行PREQUERY並加入該結果

select STRAIGHT_JOIN
      TS2.*
   from
      ( select ts.tracksimID
           from tracksim ts
           where ts.trackID1 = 168123
             and ts.sim > 0.5
        UNION
        select ts.trackSimID
           from tracksim ts
           where ts.trackid2 = 168123
             and ts.sim > 0.5 
      ) PreQuery
      JOIN TrackSim TS2
         on PreQuery.TrackSimID = TS2.TrackSimID
   order by
      TS2.SIM DESC
   LIMIT 0, 100

Answer 2

我通常都同意Drap，但是以下查詢變體可能更加有效，尤其是對於更大的LIMIT：

SELECT TS2.*
FROM (
  SELECT tracksimID, sim
  FROM tracksim
  WHERE trackID1 = 168123
    AND sim > 0.5
  UNION
  SELECT trackSimID, sim
  FROM tracksim
  WHERE trackid2 = 168123
    AND ts.sim > 0.5
  ORDER BY sim DESC
  LIMIT 0, 100
) as PreQuery
JOIN TrackSim TS2 USING (TrackSimID);

需要(trackID1, sim)和(trackID2, sim)索引。

Answer 3

嘗試過濾查詢，以免不返回完整表。 另外，您可以嘗試將索引應用於其中一個軌道ID的表，例如：

CREATE INDEX TRACK_INDEX
ON tracksim (trackID1)

http://dev.mysql.com/doc/refman/5.0/en/mysql-indexes.html

http://www.tutorialspoint.com/mysql/mysql-indexes.htm