Find least recently used mysql table index

Question

I am cleaning up duplicate indices from (innodb)tables in a mysql database. The database has about 50 tables.

While I can check for duplicate keys using pt-duplicate-key-checker, I was wondering if there is a tool that could help me find out least recently used indices from all the tables.

For eg. , if table "A" has three indices defined "index_1", "index_2" and "index_3", and out of them "index_3" is used least frequently , assume its used every 1/10000 queries made on the table, then the output of the script or tool should be "index_3".

Is there a good way or a tool that could help me run this analysis on the database?

Thanks in advance.

Answer 1

Starting with MySQL 5.6, the performance_schema instruments table io, and computes aggregated statistics by table, and by index.

See table performance_schema.table_io_waits_summary_by_index_usage:

http://dev.mysql.com/doc/refman/5.6/en/table-waits-summary-tables.html#table-io-waits-summary-by-index-usage-table

Finding the least recently used index involves time and timestamps.

What the performance schema measure is counting io against an index, so it can be used to find the least often used index, which in practice should be pretty close.

Full example here:

http://sqlfiddle.com/#!9/c129c/4

Note: This question is also duplicated in

https://dba.stackexchange.com/questions/25406/find-least-recently-used-mysql-table-index