查看mysql表的碎片率,及优化方法

查看mysql表的碎片率:

SELECT TABLE_SCHEMA
      ,TABLE_NAME 
      ,ENGINE
      ,ROUND(((DATA_LENGTH + INDEX_LENGTH) / 1024 / 1024), 2) AS SIZE_MB
      ,ROUND(DATA_FREE/1024/1024,2) AS FREE_SIZ_MB
FROM information_schema.TABLES 
WHERE DATA_FREE >=5*1024*1024
ORDER BY FREE_SIZ_MB DESC;

Myisam引擎使用下面语句优化表:

optimize table XXX

​

关于innodb的表优化,看了官方文档,要想optimize语句生效,有一些前提条件.

​​https://dev.mysql.com/doc/refman/8.0/en/optimize-table.html
​​

​​https://dev.mysql.com/doc/refman/8.0/en/alter-table.html​​

查看索引使用情况:

SELECT object_type, object_schema, object_name, index_name, count_star, count_read, COUNT_FETCH FROM PERFORMANCE_SCHEMA.table_io_waits_summary_by_index_usage WHERE object_schema = "xxx" AND object_name = "xxx"