清理MySQL表空间碎片

1. 查询碎片超过10M的表

（1）整个数据库

   SELECT

    table_name,

    round(data_length / 1024 / 1024) AS data_length_mb,

    round(data_free / 1024 / 1024) AS data_free_mb

    FROM

    information_schema. TABLES

    WHERE

    TABLE_SCHEMA = 'xxx'

    AND round(data_free / 1024 / 1024) > 10

    ORDER BY

    data_free_mb DESC

    LIMIT 10;

   (2) 单表查询

        show table status from table_schema like '%[table_name]%';

2. MyISam 引擎

    optimize table [table_name]

3. Innodb 引擎

    alter table [table_name] engine= innodb

    alter table [table_name] force;