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⑴Hander Read First:The number of times the first entry was read from an index. If this value is high, it suggests that the server is doing a lot of full index scans.

具体是指读索引的第一项即叶子节点的第一个节点（的次数）,也就是说查询从索引的根节点一直往下扫描，当这个值比较高时，说明很多的索引扫描

⑵Handler Read Key:The number of requests to read a row based on a key. If this value is high, it is a good indication that your tables are properly indexed for your queries.

具体是指是指读索引的某一项即叶子节点的某一个节点（的次数），当然包括索引叶子节点的第一个节点，当此值比较高，说明查询走了索引，这是一个好现象

⑶Handler Read Next:The number of requests to read the next row in key order. This value is incremented if you are querying an index column with a range constraint or if you are doing an index scan.

具体是指读索引的下一项（的次数），这在全索引扫描以及索引范围扫描时出现

⑷Handler Read Prev:The number of requests to read the previous row in key order. This read method is mainly used to optimize ORDER BY … DESC.

其实跟Handler Read Next读的顺序相反，通常在desc中出现

⑸Handler Read Rnd：The number of requests to read a row based on a fixed position. This value is high if you are doing a lot of queries that require sorting of the result. You probably have a lot of queries that require MySQL to scan entire tables or you have joins that don’t use keys properly.

具体指（随机）读取的行数通过一个固定的位置（位置指的是以通过[排序字段、指针]排序后的位置,该位置用来读取数据行），一般会在双路排序中出现，可以用max_length_for_sort_data来控制，一般max_length_for_sort_data=4就会产生双路排序

⑹Handler Read Rnd Next:The number of requests to read the next row in the data file. This value is high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have.

具体是下一数据行的请求数，针对数据的读取，通常值比实际大1，在国外网站这样的解释，这是实例读取数据文件的时候，产生的一次

参考文章

http://www.fromdual.ch/mysql-handler-read-status-variables

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