作/譯者：葉金榮（Email: ），來源：http://imysql.cn，轉載請注明作/譯者和出處，并且不能用于商業用途，違者必究。 1、先來看看多次刪除插入操作后的表索引情況mysql> SHOW INDEX FROM `tbl_name`; +----------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | +----------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | tbl_name | 0 | PRIMARY | 1 | StepID | A | 1 | NULL | NULL | | BTREE | | | tbl_name | 1 | FlowID | 1 | FlowID | A | 1 | NULL | NULL | | BTREE | | | tbl_name | 1 | WagerCount | 1 | WagerCount | A | 1 | NULL | NULL | | BTREE | | | tbl_name | 1 | WagerID_3 | 1 | WagerID | A | 1 | NULL | NULL | | BTREE | | | tbl_name | 1 | WagerID_3 | 2 | StepType | A | 1 | NULL | NULL | | BTREE | | | tbl_name | 1 | WagerID_3 | 3 | ParamResult | A | 1 | 255 | NULL | | BTREE | | | tbl_name | 1 | StepType_2 | 1 | StepType | A | 1 | NULL | NULL | | BTREE | | | tbl_name | 1 | StepType_2 | 2 | ParamResult | A | 1 | 255 | NULL | | BTREE | | | tbl_name | 1 | WagerID_2 | 1 | WagerID | A | 1 | NULL | NULL | | BTREE | | | tbl_name | 1 | WagerID_2 | 2 | StepType | A | 1 | NULL | NULL | | BTREE | | | tbl_name | 1 | WagerID_2 | 3 | ParamResult | A | 1 | 255 | NULL | | BTREE | | +----------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 11 rows in set (0.01 sec) 2、優化表mysql> optimize table tbl_name; +---------------+----------+----------+----------+ | Table | Op | Msg_type | Msg_text | +---------------+----------+----------+----------+ | test.tbl_name | optimize | status | OK | +---------------+----------+----------+----------+ 1 row in set (40.60 sec) 3、再來看看優化后的效果mysql> SHOW INDEX FROM `tbl_name`; +----------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | +----------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | tbl_name | 0 | PRIMARY | 1 | StepID | A | 172462 | NULL | NULL | | BTREE | | | tbl_name | 1 | FlowID | 1 | FlowID | A | 86231 | NULL | NULL | | BTREE | | | tbl_name | 1 | WagerCount | 1 | WagerCount | A | 4311 | NULL | NULL | | BTREE | | | tbl_name | 1 | WagerID_3 | 1 | WagerID | A | 86231 | NULL | NULL | | BTREE | | | tbl_name | 1 | WagerID_3 | 2 | StepType | A | 172462 | NULL | NULL | | BTREE | | | tbl_name | 1 | WagerID_3 | 3 | ParamResult | A | 172462 | 255 | NULL | | BTREE | | | tbl_name | 1 | StepType_2 | 1 | StepType | A | 9 | NULL | NULL | | BTREE | | | tbl_name | 1 | StepType_2 | 2 | ParamResult | A | 86231 | 255 | NULL | | BTREE | | | tbl_name | 1 | WagerID_2 | 1 | WagerID | A | 86231 | NULL | NULL | | BTREE | | | tbl_name | 1 | WagerID_2 | 2 | StepType | A | 172462 | NULL | NULL | | BTREE | | | tbl_name | 1 | WagerID_2 | 3 | ParamResult | A | 172462 | 255 | NULL | | BTREE | | +----------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 最后，來看看手冊中關于 OPTIMIZE 的描述：OPTIMIZE [LOCAL | NO_WRITE_TO_BINLOG] TABLE tbl_name [, tbl_name] ... 如果您已經刪除了表的一大部分，或者如果您已經對含有可變長度行的表（含有VARCHAR, BLOB或TEXT列的表）進行了很多更改，則應使用 OPTIMIZE TABLE。被刪除的記錄被保持在鏈接清單中，后續的INSERT操作會重新使用舊的記錄位置。您可以使用OPTIMIZE TABLE來重新 利用未使用的空間，并整理數據文件的碎片。 在多數的設置中，您根本不需要運行OPTIMIZE TABLE。即使您對可變長度的行進行了大量的更新，您也不需要經常運行，每周一次或每月一次 即可，只對特定的表運行。 OPTIMIZE TABLE只對MyISAM, BDB和InnoDB表起作用。 注意，在OPTIMIZE TABLE運行過程中，MySQL會鎖定表。 本文出自 “MySQL中文網”博客 http://www.imysql.cn/

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