Pruning unused indexes

Indexes can end up taking up a large amount of space in your database. This can make things like backups very large and unwieldly. Pruning unused in

Finding unused indexes and their size

SELECT t.object_name, 
    t.index_name, 
    ROUND(i.stat_value * @@innodb_page_size / 1024 / 1024, 2) size_in_mb
FROM 
    performance_schema.table_io_waits_summary_by_index_usage as t 
JOIN 
    mysql.innodb_index_stats as i 
ON 
    t.object_schema = i.database_name 
    AND t.object_name = i.table_name 
    AND t.index_name = i.index_name 
    AND i.stat_name = 'size'
WHERE 
    t.index_name IS NOT NULL  
    AND t.index_name != 'PRIMARY' 
    AND t.count_star = 0 
    AND t.object_schema = 'dbname'  
ORDER BY t.object_schema, t.object_name;

Reference:

Temporary disabling indexes

You might want to try disabling an index before actually removing them.

MySQL 8 supports invisible indexes, but 5.7 does not. The only thing you can do on 5.7 is add an IGNORE_INDEX hint to queries that would use the index, so that the optimizer doesn’t pick it.